If you're thinking about looking at bikes from REI, I'd suggest coming into the city and checking out the flagship store downtown. You'll probably have better luck there (with regards to knowledgeable staff) than at some of the other smaller stores in the area. I've never shopped for a bike there, but I have spent a good bit of time browsing around their bike department. (It's a great place to see a lot of different gear when you're doing comparison shopping...especially clothes.)

Besides, if you haven't been to that store yet, it's kind of worth it just to witness the sheer size of the place. A lot of my friends who come to Seattle just for a visit request a trip there as a tourist stop, which works for me since it's pretty close to my place. (I pass it every morning on my commute to work.)

Also, there's a Play It Again Sports right around the corner from it on Stewart. They usually have a good number of bikes (new and used) hanging around as well--lots of Marin bikes, if their window displays of late are any indication.