I also have the 720i. It's pretty good, though the software is a little weird. It downloads to the PC over IR, and IIRC, you can set up things like the training ranges on the PC and download them to the watch. It does normal cycling, and you can add cadence or power if you want it (cadence cheap, power expensive).
It tracks time in zones automatically - you get a chart that shows your whole workout and details the time in zones. All you have to do is hit the start button, wait for it to grab your heart rate, and start riding.