I love the 2.1 spa. The 30 speed gearing has a nice transition ratio between all the gears. My old 24 speed (Gary Fisher Zebrano S which is a hybrid) seemed to be missing a couple. sometimes it seemed i wish there was a gear in between. The shifters and derailers in this bike are easy to get used to, and shift very smoothly. Brakes work well and I like the quick release on the breaks (I have to remove the front wheel to hang my bike on the wall when I'm not riding). The bike is nice and light, which makes it alot easier getting up those hills. It's nice and aerodynamic down hill as well. Hit a new top speed and a new average speed on my 1st time out, and that was on a 10 mile ride, right after 10 miles of riding making seat adjustments. The dampening tape on the handle bars, front fork vibration supression and the 1/2 inch of shock on the back make for a nice smooth ride (no road vibration) and the shock helps get the rear wheel on the ground faster after hitting bumps on the road.
Downsides: I found the saddle it came with is too hard. I decided to replace that the first time I test rode it. The only other problem is the pedals are too small. I wear a size 12 sneaker. The pedal it comes with only extend 3 inches out from the crank. So small that my heels hit the frame for the back wheel. I'm replacing them with Shimano PDM-324 pedals. These extend 4 inches and are 2 sided, platform one side, clipless on the other.
One other thing Trek stopped making the 2006 2.1 SPA (according to my bike shop) so you may have to find a place that has the right size in stock before they run out. I was told they stopped to start making the 2007 version (the shop told me there would be a 2007 2.1 spa. Also Shimano has the pedals I mention on back order (for months). Apparently there isn't enough profit on these pedals. I bought mine NEW on Ebay (saved $25 over retail)

. I plan on getting clipless shoes for these pedals in the spring.
Bye the way I also test rode the TREK 5000 triple, but I found they put alot of lower end parts on it (shifters, derailers,etc). Most of what your paying is for the frame and you're not getting any savings in weight.