I must admit I do not have a Pre (still on my Treo 650). However, my girlfriend has one and we had 2 fold issue to resolve. First was importing contacts from her old Blackberry to her new Pre (not too difficult). The second was dealing with the "polluted" Contacts list (from syncing with GMail) full of random emails and "people" with no phone numbers, etc.
I came up with, what I think, is a rather elegant solution. It is very possible others have already figured this out and posted on it, but I thought I'd share my experience in case it could help anyone.
I have put up a quick webpage describing the procedure (start with syncing a Blackberry, but I'm sure you can adapt it). I can't post links because I havn't posted 5 messages yet. But you can copy/paste it into your browser.
Keep your Pre contacts and your gmail contacts Seperate
Later I'll put up a more attractive page at the same address.
Hope this helps someone,