wheel - 8:21 pm on Sep 7, 2010 (gmt 0)
Dream, I think you'll find that the answer isn't precise. You may have to experiment, and what you may find is 'sometimes it works like this, and sometimes, it doesn't'. And why it goes one way or the other, hard to say.
I've bought a drop, thrown up a wordpress default install with 0 content, and 2-3 years later it's still showing great PR. I've bought a drop and thrown up great content, and huge PR drop fairly quickly.
Use your head, use some common sense, try a few things to see what works. Buying drops, or more specifically, catching them before they drop, is a low risk business. Plenty of domains out there for $10-$20. Go get 10 and try it out.