After trying a few more caches today using the TomTom and getting frustrated by the low resolution (10 yards is the best I could narrow coordinates down to), my girlfriend (AlteredHope) downloaded the app for her IPhone 3G. We found caches a lot easier with her IPhone and could download the caches directly to it from the website.
I doubt I'll be bothering with trying to use the TomTom anymore for actual cache hunting. It will be relegated to just getting use close, if even that.
I love it for driving, but it just doesn't work very well for actual searching.