Newbie To Hardlinks. Please Explain Links Expiring.

I notice a lot of ads offering hardlinks. Many of them offer the link(s) for 6 months or a year. My question is: isn't that a bad thing? I mean...if you get a google bump for the links, don't you get a google slap for the links no longer there when they expire?

Another question: I read that Google is about to stop PageRanks (or already has?) as a part of their algorithms. So, these offers of PR3, etc. aren't a selling point anymore, are they?

Please explain (and talk to me like I'm stupid, please