One thing I'd love to see (and haven't seen in competing apps either!) - GPS support...
I'd love to have the ability to connect to my bluetooth-GPS and show my contacts where I am right now, maybe also post my current position on a map-Mashup that shows where I am on a Google- or Yahoo-worldmap.
Currently, the only way for me to do something like that is by sending an SMS with my position from TrailExplorer to Twitter...
