I've been looking at getting a TomTom 700 and today persuaded the local Halfords to give me a demo of the Remote Control facility.
Interestingly, sitting next to the 700 was a 500 and, lo and behold, the 500 responded to the remote control unit just like the 700!
So if you've got a 500 and want Remote Control, it may be worth trying to buy the one for the 700 separately.
Cheers to all,
JohnK