Y Combinator startup RescueTime lets users monitor which applications and websites they use/visit the most, and then lets them use that information to try to cut down on inefficient uses of time. It’s useful on an individual basis, and it helps businesses (who pay $4-$8/user/month) monitor what applications are being used, and where time is being wasted.

It’s also a lot of fun to look at the patters from the aggregate data.

The site has about 100,000 users and is growing 5% a week, says an investor, and 4% of users convert to a paid account. The company has also turned down at least a couple of acquisition overtures.

Instead of selling, they’ve raised their first real round of financing after the seed funding from Y Combinator – $900,000 from True Ventures, Chris Sacca, Tim Ferriss (author of the 4-Hour Workweek), Mike Seckler and Mike Koss.