Its a total myth.

Try this an an experiment...
1. Find a page on your site with some PR (say 4) and put 300 links going out on it to PR 0,1,2 or 3 sites
2. Wait for a couple of Google PR updates to see what happens to the PR on that page (you might be waiting for a while due to there being no updates for a while).
3. Make sure the incoming links to that page stay the same.

I have done this several times.
Guess what happens to the PR of the page ..... NOTHING.

Also what about the 4.5 million sites that DMOZ links to, of which 4.49 million of them have PR less than what DMOZ have ... dosen't do them any harm.

BTW - what are you doing linking to sites based on PR? You are supposed to be linking to sites, because they are of use to vistor to your site.

CBP