I am working with a friend right now (and hopefuly some help from the blackberry dev guys) to design a program that interfaces with a bluetooth GPS module, polls the current location/speed/etc data, and dumps it to a log file which then gets uploaded to a server for real-time tracking.
I am probably going to make it in such a way where you plug in your own server address/port information, and then configure it on your end for an interface into googlemaps for example. Least overhead possible, allowing as much customization as you want on your end.
My goal is to have a piece of software I can run during road trips, where my parents/friends can log onto my website, and see where I am in the past few minutes. Might help resolve some of the "how much longer, where are you, have you died yet" type of calls, or at least limit them. Since most of this stuff is transmitting or working with incredibly small text files, we are talking super low bandwidth. I could probably handle a few thousand users on my site, since the map data would be coming from google, with me just serving out plot points depending on what user it was.
Oh, and for all you tin-foil hat guys, all of this is going to be open source, so you can see exactly where your precious lat/long data is going