I currently use a USB wifi adapter with chipset Realtek RTL8192SU.
It works with no extra drivers to install in Ubuntu 64 bit 11.04. Under a light load it works fine. But when trying to watch streamed movies, it stops every 10 minutes. I don't have to reconnect, I have to just press play again to start the movie where it left off.
In Windows 7 it works fine. In a different laptop I'm using the built in wifi with Ubuntu 11.04 and no disconnects at all. I really think this adapter just doesn't work as well in Ubuntu.
I would like to know what adapter you use that doesn't freeze up on you consistently under a heavy load. Please let me know if it was an easy install as well. Thanks!