Let the hive mind of Engadget get that for you.
"As someone who doesn't reside in the USA, I was wondering what would be the best way to get internet for my computer in the US for a couple of weeks? If it were Europe I know I'd look for some prepaid data. Is there anything similar offered by American carriers? A MiFi or a data SIM that I can tether from would work, but I'm trying to maintain a tight budget. Help!"
T-Mobile continues to operate most of the Starbucks hotspots, and will continue to do so for some time. What has changed is the hotspot management, which is shifting over to AT&T. However T-Mobile users & devices (Talk Unlimited phones, WiFi digicams with T-Mobile access, etc.) are grandfathered for five years; which is longer then nearly any WiFi device folks are now using will still be used. So for all intents & purposes nothing has changed except AT&T customers can now share the WiFi too.