One thing I've used my TomTom nav. on the T3 for is to 'bookmark' shops and restaurants when I'm in a new town. Maybe I'm walking around town a Friday evening, trying to find an open restaurant to get something to eat. Often I will pass by interesting shops that I want to visit later, or other restaurants, pubs and so on. With the BT GPS in my pocket I just whip out the T3 and sets a 'favourite' in TomTom at the current GPS position. Later I can find it again. TomTom isn't really suited for this though, because the maps keep rotating when you try to find the way to the address later (rotating maps are good for driving, terribly for walking).
I don't know if "bookmarking" is possible in Mamo Mapper, but it's one of the more useful uses of GPS applications IMO.