I had the lockup happen to me yesterday with my nice new AE + connected disk.
It happened when I was trying to backup a 6GB Parallels image to the airdisk. The disk just disappeared/unmounted although the wifi indicated on the bar showed I was still connected. I could not access anything on the internet though, and had to power cycle the AE.
I found other references to people having problems with transferring lots of data (or lots of large files), but no matter what causes it, it means that I cannot count on the AE/airdisk to be a decent backup drive.
Anyway, were you using the airdisk when you see the connection problems? If so, you might be seeing the same thing I did.
Mike