There is no official version of Android 3.1 for Asus’s Eee Pad Transformer available jet. Today Asus will announce new devices (the Padfone). In context of this announcement it is very likely that Asus will reveal some further details for the rollout of Android 3.1.
For those of you who cannot wait for these official updates there is the possibility to download the 220 MB large ROM manually (but it is not sure yet if this version will be the final release). The ROM image is compied on the SD card and installed via the Bootloader. To do this you have to shut down the Tablet and press “Volume” and “Power” button on the same time. After this you have to press “Volume up” within 5 seconds of time – otherwise the phone will reset to manufacturer settings.
Android 3.1 includes better performance and enhanced task bar as well as resizable widgets. Problems during installation of the custom ROM are not known.
The rooted version can be found at: http://forum.xda-developers.com/showthread.php?t=1101717