This weekend I bought my first bike since...well, since my favorite accessory was pom-poms for the handles. I shopped at several shops, including REI and Gregg's, but ended up buying from Bothell Ski & Bike.
A lot of the decision had to do with the bike itself; it was more comfortable and rode better than the others, but I was much more able to determine that at the Bothell shop than anywhere else I'd looked, because the shop is just off the Burke-Gilman trail. They just traded the bike for my car keys, and said, "Go ride!" The trail provided hills and straight areas, and I didn't feel any pressure to return quickly.
In contrast, testing at Greggs involved filling out a form, handing over a credit card and my driver's license, and navigating the car-heavy streets around Greenlake. For a new cyclist, that's intimidating. And testing at the other shops was just a matter of two or three turns around the parking lot. I suppose REI might have been better, if there had been even a single staff member around to help and answer questions about the bikes.
But at the Bothell shop, the staff were friendly and helped with every question, and I felt like I was buying from knowledgeable folks who cared about more than selling the most expensive item.