I have used Tom Tom Rider (my Dad's) and PDA-based Tom Tom (my own) on my 996 and on my 250 trail bike.

Largely very good, I have just a few gripes:
- TT Rider audio is too quiet. PDA version is slightly better.
- Both units would be better if they gave instructions a bit earlier
- no off-road tracking

I am really interested in the Quest 2 - tell me more SazzaJ