Without going back to the sites I looked at, I know one thing I thought about was maintenence -- I'll be taking a bike maintenance class at my local shop, but I'll be starting from almost zero knowledge
If you start with a bike in good condition, everything adjusted and tuned to perfection, then you can almost forget about working on the bike during a summer long trip.
I agree to the tune of about 75%. The other 25% includes fixing a flat tire (betcha'll get to do that!). You'll need to understand how your brakes work, so you can take up the slack caused by wear -- unless you find a bike shop every couple weeks to check it for you -- and watch the brake pads so you can get them replaced if/when necessary. It's also a good idea to know how to fix a broken spoke (hint: get a FiberFix), and at least roughly true the result until you can find a good bike shop to get it just right.
Building a bike up from the frame can be fun, too, but as Russ notes, it's not usually necessary.