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.
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.
The "rel" attribute
As of 18th January 2005, Google, together with other search engines, is recognising a new attribute to the anchor tag. The attribute is "rel", and it is used as follows:-
a href="http://www.domain.com/somepage.html" rel="nofollow">link text (/a>