As a note, the 500, unlike most of the other units, won't run while it's on charge.
Worth pointing this out again. Also, with the way it mounts and the location of the socket it'd be pretty hard to get a plug in there to power it while you had it mounted.
It does just about everything else you could want, really easy to swap between bikes as well.
One word of caution if you decide to buy a speed and cadence sensor they don't work on some dual suspension rear swing arms. I have a SC Heckler (my XC bike) the design of the rear swing arm means i cant mount the sensor to get both speed and cadence.
Id say there wouldn't be a problem on a HT
It's kindof an annoying design, the sensor. On the upside, it does make singletrack speed/distance sensing a lot more accurate. On the downside - mounting it is kindof fiddly. If your cranks are the wrong shape or whatever it can take a bit of bodging-up a mount to get the crank magnet detectable by the sensor whilst you can still get the wheel sensor in a good spot.
The sensor only adds about $50 to the price if you purchase it as a bundle, which is OK.
What isn't OK is that my sensor started chewing through batteries after a couple of months, and recently stopped working completely. I was only using it about once a fortnight, too. I'm about to see how good CRC's warranty returns are..
As for the computer doing everything you want, given it's a GPS it'd be good to know my Lat/Lon. It just won't show you - they're not one of the selectable display fields. It will tell you which direction (N, NE, E, SE etc) you're going, plus the usual speed stuff..
Lastly, the unit isn't completely waterproof. It got rained on for a while (riding in the rain for maybe an hour) and it had a little steam on the inside of the screen that night. I always make sure the usb-port cover is on right, but it's not exactly a snug fit. The unit has been rained on a little since, and has been OK though.