I've been a long time user of Bloglines, but I kept hearing good things about Google Reader and decided to give it a try…
Well, I'm a convert. The switch was fairly easy - just export OPML from Bloglines and import into Google Reader. The main selling point for me is the keyboard shortcuts. One feature I do miss is the ability to mark posts unread and have them treated in a special way (Bloglines would indicated posts you've never seen separately from those you've seen but marked unread).
I'm impressed that Google went back and made a product that was entirely unremarkable into one that is very usable with a second release. That's unusual for a Google product.
Anyway, I'm a Google Reader user now.