I have a rt2500usb adapter (Gigabyte GN-WBKG) that is now working excellently with 2.6.28 and beyond, many thanks!
The issue I'm having (running 2.6.29 on x86) is that the LEDs do not behave as expected. The activity LED never activates, and the link LED is always lit when the interface is up, irrespective of whether a link is actually established or not. I didn't find any reference to an outstanding issue with this, so is this somehow by design, or is isolated to the particular model somehow?
Please check compat-wireless from linuxwireless.org and see if a more recent version of the driver behaves better.
I did make some changes to the LED handling, and that could have had different results for various people.