I did a little experiment. Took an old gpx file recorded with non Garmin device (Globalsat bt-335, a simple bt gps logger I used also today in live tracking) and converted it to AP sessiondata format and added it to sessiondata field and submitted to AP. It all went nicely, take look:
http://www.attackpoint.org/viewlog.jsp/user_954/pe...
I am not sure does Ken like I do experiments like this (well, I'd say giving me beta testing privileges is kind of asking for it), but anyway as far as I see this all is done in a pretty nice way. Garmin plugin is made by Garmin of course, but the rest is done in a smart way, I can see this gps feature will not cause too much additional load to AP server (it goes to client browsers and google servers and they take can it happily) and it is easy to add support to any format or even allow third party converter (like the one I just wrote to do the experiment) copy paste based session data posts or what ever. Typical AP style solution, if you try to figure out a really smart way to do something Ken does it just a little bit smarter way.