With a few talking about using SSD drives in a Tivo, I got curious and started looking around and found the better idea might be the combo ssd HD drives. The Seagate model uses adaptive technology that caches the common used read only data on the ssd area while the rest exists on the standard HD area. The the drive it's self appears as a single drive and the adaptive algorithm is built-in to the drive which is transparent to the user/device.
Only thing I can see is faster reboot of your Tivo and possible better menu reaction, the other issue is that the drive in a standard PC requires several reboots to properly cache the common used data on the solid state area so it might require you to reboot your Tivo a few times after the drive is installed.
This might enhance the older TiVo's, anyone want to test this?
2tb drive on Amazon ($119):