It's just a little app that stays on the system tray, takes about 5 megs of RAM, and every half hour (or other defined time period) it polls the system for the uptime and sends it over to the site. Doesn't do absolutely nothing else besides that.

But one thing to be aware of is that if you want to put several machines on it, you have to create a separate account for each. Using the same reg data on several machines at the same time will get your values all screwed up.
That's why you see people with two and three accounts there but with different names.