I am a Uverse user and up to now have been pretty happy. While I am unlikely to exceed this cap, I don't appreciate having to pay for "full service" and getting something less in return (by being limited and penalized for using too much....).
I have a planned move coming up later this Summer and this will likely result in me dumping Uverse at my new address. Not cool on AT&T's part.
I am sure this is meant, more than anything else, to limit using the 'Net for TV and movies, vice getting from AT&T.