From the Virgin Media Community Tivo forum (and posted on other blogs too), here's a list of what was delivered with the recent "Third Tuner" software update on the TiVo boxes:
•3rd Tuner support
•Recommendations improved by incorporating customer collaborative Thumbs data into the Discovery bar and recorded recommendations
•Box no longer displays ‘Channel not authorised’ during normal channel changes
•Customers no longer PIN challenged on watershed compliant channels
•Bookmarks supported in Movies
•Trailers now available and working for movies
•STB no longer reboots when return path is lost.
•Green button now links to catch-up content correctly
• Music playlist fixes
• Metadata improvements
• Quicker to restore TV service after reboot
• Medium description utilised in VoD screens (adds rating guidance information)
• User presented with choice of HD or SD assets in ‘Get from On Demand’ screen
• Front panel LED’s now function when box is in standby
Also, HD capacity now shows at 125 hours rather than 99.