Online log?

[kerrypolka]

I'm looking for an online weight lifting log that will let me enter what I've done, eg "Bicep curls, 3 sets of 8 reps, 6kg weights" and:

track my improvement

give me encouraging stats like, "Congratulations, that's 35% more than you could lift when you started!" and "Great job - that's 15% of your bodyweight!"

Does such a thing exist? I want to start keeping a log, but I lose paper all over the place and if I start a paper journal I won't keep it up. An Android app would also work, but I'd prefer online!