Now, unless you already know, StackOverflow is a brilliant place for developers to ask and answer questions about programming and related stuff (Joel from Joel on Software was one of the startup guys, a brilliant guy I've had the pleasure to meet at some geeky event in Oslo a few years back). Even the question above was on the edge of that criteria, so that's how hardcore the programming focus is. However, I did write an answer based on years of experience with a brain that never seem to shut down which I'd like to share, because only yesterday I was once again asked this very question, so I need to share ;
I use the last 5 minutes of my day to write myself a debrief note for the next day. This will do three important things;Read the rest and fuller response at StackOverflow.
It takes your mind off the complexities as the debriefing will be a short form of all the things you've worried about, and helps clear the mind of all the what-if things.
If your mind have a long down-settling time, the debrief note is the perfect place to use for a central of "things I forgot about" or should note somewhere. The debrief note becomes a knowledge central for whatever you did that day.
It focuses your mind on the real issues. One thing is to clear the mind, another is to let it keep going, but more focused. So even if your conscious mind is letting go, it's probably a good idea to let your unconscious mind keep churning at the problems, and a good way to help your mind do this is to be slightly futuristic in your notes (thoughts on direction, for example).