Axiom, based on personally working on thousands of Trek's entry-level aluminum bikes, there's no need to be concerned about the durability of the frames (in real life, that is). They also have a lifetime warranty, but your chances of needing that are approximately zero, judging by my customer base.

30% off is a great deal, too. They're probably basing that off the advertised MSRP, not the suggested MSRP, but it's still a great deal in a business where we basically make nothing on bikes after overhead. Go for it. Throw your LBS a bone by buying some accessories to go on it, maybe some lights and a computer.