Just signed up and started playing around with it (although I agree with snitko, there needs to be something pre-signup to tell you what it is). When I went to log activity, it said "Work done", with a '0' in the field. This doesn't tell you what you're measuring, which I believe is a problem. For instance, is this lines of code? Is it the number of goals I met? Can I type in what I did and have it log that?

Needs more user direction, but I like the idea and I'll certainly keep an eye on it.

Edit: Also, OpenID support would be nice, but is not a dealbreaker by any means. Nice work so far, for sure.