I had not used my MacBook at home under OS X for a while because it had temporarily became my main computer at work using Windows XP under Boot Camp. A few nights ago I booted it into OS X to do some browsing and the internet was so slow under OS X that I rebooted into Windows XP (Sad, I know ). I had experienced the same type of slow connections before at Starbucks but could never figure out the cause.
Tonight I had the same issue and was determined to figure out what was going on. There were a few suggestions out their about renewing your IP Address and rebooting your system, which I tried to no avail. Others said to reinstall OS X to try to fix it which I thought was going to far. Finally someone suggested changing the channel that your router was broadcasting on to try to fix it.
Previously I had a Linksys router that in between it and my computer was a microwave. Every time the microwave would go on I would lose my internet connection. When the microwave turned off the internet would come back on. While investigating that issue someone had suggested changing the channel on the router to a higher channel and sure enough that worked for the microwave issue.
I am happy to say that changing the channel on my Airport Extreme router fixed my MacBook slow Wifi issue as well.
The place to change it in the Airport settings was under Airport and then Wireless and then about half way down is the channel selector. Mine was set to Automatic and was on channel 1. I selected channel 10 and then once the Airport rebooted I had a speedy internet connection on my MacBook via Wifi.
This obviously won’t help me at Starbucks but it is possible that if I have this same issue that I can call their tech support and they can hopefully VPN in to change the channel. I had issues with T-Mobile at Starbucks before and their tech people helped me out so I would hope that AT&T would do the same.