I'm sure if anyone hits this cap and you're doing legit, bussniess, entertainment type things all you will have to do is call up CS, tell your story "I recive 10mb PDF's all day from my art department" and they'll uncap you.
This is just in place to prevent people from abusing it, like oh i don't know, hosting a web server via their phone.
And lets note that this cap is for 3G over the air, it shouldn't count if you're connected via wifi.