ASUS' official Android 3.1 update is not out yet. But Eee Pad Transformer now cxan get their 3.1 update early. Looks like the final version of the 3.1 update leaked out over the internet. User reports that performance and general responsiveness have been improved. For more details you can download and try it for yourself.
To flash,
1. Extract EP101_SDUPDATE.zip from the above .tar file
2. Place it on your SD card
3. Make sure the Transformer is plugged in or has at least a 50% battery charge.
4. Power off
5. Press the volume down key and power key at the same time and continue to depress both until you notice a ROM Boot screen that advises you to press the volume up key within 5 seconds to start the ROM update process.
6. Press the volume up key and the unit will update and reboot. It should take about 3~5 minutes
7. After a reboot, a user notification should arrive in five minutes or so that the docking station has a firmware update available to version 0209. Please follow the instructions and update the docking station and then complete another reboot. The 0209 firmware offers improved typing speeds, mouse tracking and USB compatibility.
Source