Trying out toggl for some work I am doing with two other people. It's ok, has some useful functionality, but it's not great. I don't like how the tasks are stuffed in a small panel over on the right. There is a timer here, which is a nice idea, but twice now I've left the timing running over night which means I just have to go back and estimate my times.
I think that basically it's just not simple enough – I spend too much time thinking about how to use it properly. I'll do a proper usability analysis on it sometime soon, but I think it's fulfilling the needs of the people who wrote it, but not fulfilling my needs.
Back to the ol' 37signals maxim of build it for yourself – I'll have to build one for myself (using rails 3.0 beta I think...)