I have a Trek 7100. I bought it four years ago and it's been my regular ride ever since. It's been a good bike. The only work I've done to it was replace the rear wheel (kept popping spokes), replace the saddle (the stock one was too big & mushy) and replace the tires as they wore out. Unless you're a heavy guy the stock rear wheel will probably be fine. I had to replace the wheel because my weight exceeded the maximum weight the bike is rated to handle. That's not Trek's fault - it's mine. I should have done better research.
I do wish I had bought a bike that did not have the suspension fork. Since I only ride on pavement the fork really doesn't accomplish much. It also bounces a bit when I'm standing on the pedals trying to get up to speed.
I'm also not keen on the grip shifts. While they looked like a good idea to me before I knew any better, I now rate them as a pain in the butt. If I'm standing up and trying to get up to speed quickly (crossing a busy intersection, say), I have to make sure that my hands are nowhere near the shifters or else I'll find myself unexpectedly changing gears - which can be a problem.
Now for the good.
Aside from the above-listed problems, the bike has been great. It has never let me down. For the last three months I have been using it as a commuting bike. I have a 40 mile round trip commute. The bike eats up mile after mile without complaint.
I'm currently researching bikes with an eye towards replacing the 7100. It's not that it's a bad bike, but it's really not built for what I do with it. There are aspects of the bike that I thought were great when I bought it that are a bit problematic for me now that I'm commuting on it.
The handlebars don't offer enough hand positions. I am on the bike three hours a day. It would be nice if I had some options along those lines.
The riding position is too upright for me now. While that wasn't a problem at all when all I did with the bike was pleasure ride, on the commute it becomes a problem on windy days. It would be nice to assume more of an aerodynamic position on windy days.
The chain stays are a bit a short for me. I wear a size 13 shoe and have some Wald fold-up baskets mounted to the rack. I had to do some creative mounting to get the baskets far enough back for me to avoid hitting them with my heels while pedaling with the baskets in use.
There again, none of these issues are the manufacturers fault, nor are they problems with the bicycle's design. They are issues for me because I'm using the bike in a manner for which it wasn't intended.
I'm looking at a touring or cyclocross bike as my next commuter.