TomTom is a great product. I never used to believe in GPS road navigation until I saw it. It is really great. Not relevant to aviation though.
Chuck is 100% right of course. It is silly to chuck out
the best nav device known to man. By all means don't use it if you don't feel like using it (on a Private Flight one is legal if navigating by tossing a coin, 10deg left v. 10deg right) but one can't make an argument against GPS on technical grounds. Some of the original (10 year old) GPS receivers were indeed cr*p but that's not relevant these days.
I would avoid a bluetooth connection between the GPS receiver and the PDA. It does work a lot of the time but some combinations are not reliable. Especially if one powers the PDA down and powers it back up again, expecting the PDA to recover the protocol. For best reliability, get a GPS receiver with a USB or RS232 cable.