I often found myself doing random stuff and then wondering "what the hell did I do?" at the end of the day. So I wrote a simple tool Smacklet http://smacklet.com/ and it has helped me immensely. All you do is: type in few words about what you are doing and plan to do now. Doing this simple exercise, I found myself more "aware" through the day and hence ended up squandering less and less time.

Give it a try if you feel like. I had several features planned, like graphs etc... but I found the current feature-set sufficient for my needs.