The value of outbound links is divided by the number of them on a given page.
A given page's PageRank is raised by the number of inbound links pointing to it.
The value of each such Inbound Link is affected by:
If you had a link to your page from a page on ibm.com that had a PageRank of 7, and there were no other links on that IBM web page, the link would have a significant effect on the PageRank of your page.
If you had a link to your site from a page with a PageRank of 1 and there were many other outbound links from that page, the Inbound Link would hardly effect your PageRank at all.
Still pretty much every Inbound Link adds up. So keep them coming.