Outbound links are a drain on a site's total PageRank. They leak PageRank. To counter the drain, try to ensure that the links are reciprocated. Because of the PageRank of the pages at each end of an external link, and the number of links out from those pages, reciprocal links can gain or lose PageRank. You need to take care when choosing where to exchange links.

When PageRank leaks from a site via a link to another site, all the pages in the internal link structure are affected. (This doesn't always show after just 1 iteration). The page that you link out from makes a difference to which pages suffer the most loss. Without a program to perform the calculations on specific link structures, it is difficult to decide on the right page to link out from, but the generalization is to link from the one with the lowest PageRank.

Many websites need to contain some outbound links that are nothing to do with PageRank. Unfortunately, all 'normal' outbound links leak PageRank. But there are 'abnormal' ways of linking to other sites that don't result in leaks. PageRank is leaked when Google recognizes a link to another site. The answer is to use links that Google doesn't recognize or count. These include form actions and links contained in javascript code.

Form actions
A form's 'action' attribute does not need to be the url of a form parsing script. It can point to any html page on any site. Try it.

Example:
<form name="myform" action="http://www.domain.com/somepage.html">
<a href="javascript:document.myform.submit()">Click here</a>

To be really sneaky, the action attribute could be in some javascript code rather than in the form tag, and the javascript code could be loaded from a 'js' file stored in a directory that is barred to Google's spider by the robots.txt file.

Javascript
Example: <a href="javascript:goto('wherever')">Click here</a>

Like the form action, it is sneaky to load the javascript code, which contains the urls, from a seperate 'js' file, and sneakier still if the file is stored in a directory that is barred to googlebot by the robots.txt file.

The Google toolbar range is from 1 to 10. (They sometimes show 0, but that figure isn't believed to be a PageRank calculation result). What Google does is divide the full range of actual PageRanks on the web into 10 parts - each part is represented by a value as shown in the toolbar. So the toolbar values only show what part of the overall range a page's PageRank is in, and not the actual PageRank itself. The numbers in the toolbar are just labels.

Whether or not the overall range is divided into 10 equal parts is a matter for debate - Google aren't saying. But because it is much harder to move up a toolbar point at the higher end than it is at the lower end, many people (including me) believe that the divisions are based on a logarithmic scale, or something very similar, rather than the equal divisions of a linear scale.

Let's assume that it is a logarithmic, base 10 scale, and that it takes 10 properly linked new pages to move a site's important page up 1 toolbar point. It will take 100 new pages to move it up another point, 1000 new pages to move it up one more, 10,000 to the next, and so on. That's why moving up at the lower end is much easier that at the higher end.

In reality, the base is unlikely to be 10. Some people think it is around the 5 or 6 mark, and maybe even less. Even so, it still gets progressively harder to move up a toolbar point at the higher end of the scale.

Note that as the number of pages on the web increases, so does the total PageRank on the web, and as the total PageRank increases, the positions of the divisions in the overall scale must change. As a result, some pages drop a toolbar point for no 'apparent' reason. If the page's actual PageRank was only just above a division in the scale, the addition of new pages to the web would cause the division to move up slightly and the page would end up just below the division. Google's index is always increasing and they re-evaluate each of the pages on more or less a monthly basis. It's known as the "Google dance". When the dance is over, some pages will have dropped a toolbar point. A number of new pages might be all that is needed to get the point back after the next dance.

The toolbar value is a good indicator of a page's PageRank but it only indicates that a page is in a certain range of the overall scale. One PR5 page could be just above the PR5 division and another PR5 page could be just below the PR6 division - almost a whole division (toolbar point) between them.

To a spider, www.domain.com/, domain.com/, www.domain.com/index.html and domain.com/index.html are different urls and, therefore, different pages. Surfers arrive at the site's home page whichever of the urls are used, but spiders see them as individual urls, and it makes a difference when working out the PageRank. It is better to standardize the url you use for the site's home page. Otherwise each url can end up with a different PageRank, whereas all of it should have gone to just one url.

If you think about it, how can a spider know the filename of the page that it gets back when requesting www.domain.com/ ? It can't. The filename could be index.html, index.htm, index.php, default.html, etc. The spider doesn't know. If you link to index.html within the site, the spider could compare the 2 pages but that seems unlikely. So they are 2 urls and each receives PageRank from inbound links. Standardizing the home page's url ensures that the Pagerank it is due isn't shared with ghost urls.

The Google toolbar
If you have the Google toolbar installed in your browser, you will be used to seeing each page's PageRank as you browse the web. But all isn't always as it seems. Many pages that Google displays the PageRank for haven't been indexed in Google and certainly don't have any PageRank in their own right. What is happening is that one or more pages on the site have been indexed and a PageRank has been calculated. The PageRank figure for the site's pages that haven't been indexed is allocated on the fly - just for your toolbar. The PageRank itself doesn't exist.

It's important to know this so that you can avoid exchanging links with pages that really don't have any PageRank of their own. Before making exchanges, search for the page on Google to make sure that it is indexed.

Sub-directories
Some people believe that Google drops a page's PageRank by a value of 1 for each sub-directory level below the root directory. E.g. if the value of pages in the root directory is generally around 4, then pages in the next directory level down will be generally around 3, and so on down the levels. Other people (including me) don't accept that at all. Either way, because some spiders tend to avoid deep sub-directories, it is generally considered to be beneficial to keep directory structures shallow (directories one or two levels below the root).

ODP and Yahoo!
It used to be thought that Google gave a Pagerank boost to sites that are listed in the Yahoo! and ODP (a.k.a. DMOZ) directories, but these days general opinion is that they don't. There is certainly a PageRank gain for sites that are listed in those directories, but the reason for it is now thought to be this:-

Google spiders the directories just like any other site and their pages have decent PageRank and so they are good inbound links to have. In the case of the ODP, Google's directory is a copy of the ODP directory. Each time that sites are added and dropped from the ODP, they are added and dropped from Google's directory when they next update it. The entry in Google's directory is yet another good, PageRank boosting, inbound link. Also, the ODP data is used for searches on a myriad of websites - more inbound links!