thanks for the filename to search for. copying the directory
rtl8192su_linux_2.6.0002.0708.2009/firmware/RTL8192SU (containing rtl8192sfw.bin)
into /lib/firmware, unplugging the usb adapter and putting it back in worked great - instant N connection.
Didn't need any kind of kernel patch with 2.6.31-16-generic - I think we just need to get the firmware added to restricted modules (if restricted???) and folks can use this adapter.