tedster - 10:02 pm on Aug 23, 2012 (gmt 0)
You do not lose any PR on outbound links.
I don't think that's exactly true - at least from the original PageRank formula (the only one we know for sure).
In the initial computation of PR, each link on a page votes for its target URL, weighted by a fraction of the page's original PR calculation. So far, nothing lost from the page itself. However ANY link from the page, internal or external is getting slightly less PR voted to it when another link gets added to the page.
So far so good the PR of the linking page itself is not affected. However, PR has always been an iterative calculation - it gets made over-and-over again around the entire web until the calculated numbers reach a threshold and stop changing enough to make a difference. Conjecture has been that this is at least a single number with a 10 digit decimal.
So on each iteration, each loop of calculation, there IS a slightly smaller fraction of PR returning to the linking page. It's not major at all, but it does exist.
Counteracting that naive, original math, we know Google has modified PR quite a few times over the years. We also have heard that links now get weighted according to their location on the page - the "reasonable surfer" model. And further, Matt Cutts has told us that the overall algorithm contains factors that can REWARD sites for linking out.
So ultimately, we get what I think of as a "no problemo" effect for helpful external linking. However, it also takes more than the conventional PR calculation to get there.