+1 on trying out bikes at the LBS. While you might not get as much of a feel as you would on a 20 mile ride, it can still tell you a great deal. For example, I was looking for a new commuter bike recently. I tried comparable bikes from Raleigh, Trek, and Kona - all labeled 58 cm. The Raleigh felt cramped, the Trek was ok but the Kona felt great. These were all lower end hybrids with 700c wheels. Needless to say, I'm now riding a Kona Dew