My Asus N13 USB adaptor (0b05:1784) worked out-of-the-box under OpenSUSE 11.4 using the rt2870sta kernel module. However, it would only operate at 804.11g (maximum speed of 54Mb/s) and no amount of tweeking could get it to 804.11n (270Mb/s).
Googling produced confused results with many people reporting the same speed restriction under Linux. I eventually compiled my own rt2870sta module using a newer version of the Ralink/Asus driver only to find the adaptor was no longer recognized.
It appears that Ralink (who make the chip and write the driver) now support the the chip under a newer driver family - 3070sta - and this supports the faster 804.11n.
The really good news is that the rt3070sta module can be found in the OpenSUSE repositories (Index of /repositories/driver:/wireless/openSUSE_11.4) and that it not only works out-of the-box but gives a reported 270Mb/s. It’s certainly much, much faster. Many thanks to the guys who put this together.
Just download and install the package using YAST/zyppper. The only extra thing I did was to blacklist the original rt2870sta module to ensure there was no conflict between the two drivers. And ignore the fact that the new module actually reports itself as rt5370sta - just part of Ralink’s weird numbering system.
I hope this will save others the hours I spent tracking this down.