Fitness is a ridiculously profitable niche. They don't need that many users to reach profitability. The margins for stuff like P90X, supplements, and powders is enormous. People who are into fitness spend $1000s per year on it, and they should be able to tap nice piece of this market.
It'll be interesting to see if this actually does take off...in its current state though for firefox a lot of the ajax elements conflict and make for a terrible experience when trying to log activities which is why I stopped bothering with the site.
This made me feel like I really need to work out. Sadly, judging by my history, my motivation for going to the gym lasts about five weeks. I've done boot camps for upwards of 18 weeks, but injured myself so badly that I had to stop.