I've been test riding a few bikes but quite frankly, except for adjusting height I haven't bothered "dialing" them in. I looked in the beginner thread and saw nothing, except to ride bikes before asking questions. I'm fairly settled on the two bikes below, it's more of a question of figuring out which size is best for me.
I'm going to buy a bike this weekend. Both bikes(Gary Fisher Marlin, Specialized Rock Hopper; I expect it will come down to 29'er vs. good brakes and lighter weight), they both fit a little "longish" compared to others I've ridden in size 17"(usually having a 580mm top tube) such that I've thought about going with the smaller models, with the 15.5" models having about a 570mm top tube, and the 17.5" models having a 600mm top tube.
Before making the final decision, I'd actually like to ride them like I will when they are mine, i.e. a good fit. So to me, that would be a 10cm stem on the 15.5" and a shorter stem on the 17.5". I'm only looking at $600 bikes, but will shops swap the stem for me before a test ride and allow me to adjust the setback for test rides?