I've been using it for a couple of weeks and it's been fun to see where my time goes. I was surprised that I don't actually spend much time during the day goofing off or reading industry news. Most of my time is spent in Outlook reading and sending email, with a lot of time spent in Excel as well.
The key to making RescueTime useful is the ability to tag sites so that you can see how your time is spent. Outlook might be tagged with "work" and "email" while GMail might be "personal" and "email". Add up all the different tasks marked as "work" and you can start to see how you spend your day.
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The product is new and is being enhanced rapidly. Nevertheless, it's easy to think of features I wish it had: auto tagging of various websites using regular expression,, track computer idle time/screensaver time as a separate entry in the logs, be able to enable/disable automatically during various times so you can only track work hours, for example.
As for me, of the 5 hours I've spent in the office today, I've spent 40 minutes in Outlook, 35 minutes on Google, and 35 minutes working on AdWords campaigns in AdWords Editor. The hourly graph has a big dip where I went for a workout (and the computer was idle). Nice.
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www.RescueTime.com