I just checked out the Trek FX a couple of weeks ago. A really nice bike. Fast and light. I really wanted one, until I rode the DS. If I were riding all smoother roads, the FX would be a great ride. However, where we ride, we have LOTS of county maintained roads which are rough gravel roads. Plus the main roads are rough and in severe need of repair. Plus we do a fair amount of dirt roads/trails and gravel roads. (Rural Georgia)
I said that to say this: do your research, ride several bikes, and choose the one that fits your needs best. To me, it's all about finding the best bike for the type of riding you do with the least amount of compromise. Of course, considering this while trying to keep it in your budget.
One thing I found helpful was the "compare" function on the Trek website. You can instantly see the difference between the various bikes.
When doing your shopping, as others have already said, pay special attention to the staff at the bike shop. We have a great shop, and it is a pleasure doing business with them. They are very professional, friendly, offer good pricing, and have a complete stock of bikes and accessories. I be able to save a few dollars elsewhere, but I like the staff and their way of doing business.
Good luck in your search and be sure to let us know what you decided on.