Both, of course!

For now I just want something to keep track of my mileage and average speed - for rudimentary training purposes (weight lost mostly). Later I'd like to have some nav ability - but I've been pretty content so far to just wing it. If I get into heavy-duty touring I'll probably get a GPS or some fancy mobile doo-dad.

Thanks for all the responses! Lots of good info from what I can tell.