This is a pretty cool idea, and I think I'll try it out for a while and see how it works. About my only reservation has to do with the limited number of parameters they're tracking: all the ones I've seen during the signup process do look like plausible correlates to happiness, but there aren't very many of them, and I think I've seen them all before in happiness research. I think I'd like to see more, to increase the chances of finding some novel correlations; of course, I suppose there's a balance to be struck between granularity and usability.

The sliders in their interface aren't playing particularly nice with my Android, either, but that's a nitpick.