@rwalterk--
My friend is on AT&T and he is *always* going over his monthly data cap. One time it was like a week and a half into his time...
I would think that using tethering would a) eat a lot of your data and b) get AT&T pissed off and they might can your contract.
But I definitely get what you're saying. My data speeds can be impossibly slow. In fact, I spent over an hour trying to load a page today just pressing refresh whenever I saw it had timed out. I was watching TV, so it wasn't like I was really in *need* of the site, but still. I get where you're coming form.