QuakeLive is my drug of choice.

This probably belongs in a meta thread: I've also been concerned that the design of Lesswrong itself encourages poor use of time. It's set up with goals similar to other content sites: Lots of high quality comments, a semi-regular turnover of the front page, and even more on the 'new' page. easy tracking of long complicated threads.

All this is perfect if you're reddit and you want tons of ad views of content your users spend hours creating. This is less perfect if you want to maximize the productivity of your users.