I ha e AT&T uverse and I went to starbux this morning and tried to log in just to see how well it worked. It went to the login screen and then as I was typing my username it dumped out, then I went into it again and before I could log in it would dump me again. I don't know if it's that starbux but my experience was not good. Luckily i can just tether my droid.
I have been in 3 different Starbucks and have not had to do anything other than connect to the wifi, no login, nothing. This was the 1st week of launch, but in any case, I've never registered at any Starbucks that I know of. It also worked in my local B&N this weekend.
Are we sure that ATT can tell the difference?