When I upgraded to 12.04 I suddenly started experience really slow download speeds with my wireless adapter. I'm using a PremierTek PT-H10DN, which uses the RTL8192SU chipset. Since it worked perfectly out of the box with 11.10 and the trouble started as soon as I upgraded, I'm assuming this is a driver issue. I downloaded a driver from the RT site, but when I try to install it it asks for authentication and then says authentication failed. Not sure why this is, or if installing this driver will even fix the problem.
I've come across a lot of posts of people complaining of the same issue with different wireless adapters. I tried most of the fixes, e.g., disabling IPv6, but none of them fixed my problem.