I got an APC USB power extender thing for like 8 bucks. It 's tiny and sits in my bento box. I tried it once to make sure it works, but my rides usually aren't more than 4 hours. I'd bring it if I was expecting a 6+ hour ride though.

The garmin is a great gadget, the data it collects is awesome. Sadly, no one really has great software to take full advantage of it. I paid for the motionbased upgrade with the 2-1 deal they're running, I've tried sporttracks and the free software that comes with the garmin. What I really want is software that'll let me lasso a section of ride and have it calculate the metrics based off the data in that custom segment. That way I can get fairly precise time / hr / climb stats for calculating power outputs etc. (geeky yeah)

The google earth thing is pretty neat, but it just lays out the route, it'd be cool to get stats in there.

Anyway, with the way it seems these things are taking off, better software shouldn't be too far away.