Pagerank is sucha n elusive creature, I have begun to use Mozilla and I haven't benn seeing page-rank for 3 months now. I look at it when I do my monthly marketing reports, I reference it once in general client stats and thats it.
To me it is valuble as a tool to talk with other webmasters about, the client cares little about a green bar they never pay attention too. They look at traffic and cash flow.
My point is that if you get lots of incoming links, without looking at PR yours will go up.
I have never paid for a link (except directories) and I just wont, I don't believe that it is useful.