I'm using an Edimax Wireless USB dongle (model EW-7711UTN) on Windows 7 64-bit. The dongle works brilliantly (it was truly plug-and-play) except for one thing.
I've noticed that if the dongle is plugged in whilst I'm logging on to Windows it introduces a massive delay - after I type in my password and hit enter, Windows shows the "Welcome" screen, then the screen goes black for 2 minutes or so (with just the cursor showing) before finally displaying my desktop. If I unplug the dongle before I enter my password, Windows goes straight to my desktop.
Even though the dongle didn't appear to need drivers for Windows 7, I did try downloading the latest ones from the Edimax website, but that made no difference.