Version 4.8.04-03 dated 27th May 2011 has turned up and here's where you get it:
Instructions on both upgrading and downgrading are on the Latest Firmware page, but I would tread very carefully with this particular beta firmware release. It's got new bad bugs in it such as crashing more often, not letting you log into Sky Player (no loss there then!), the GUIDE button often not working (use "0" instead) and it fails to pause live TV (it pauses it for a few seconds and then resumes).
However, its one small saving grace is that it doesn't repeat the previous remote control button anywhere near as much as the current stable release.