The wonderful Jessica Brockmole sent me this a few days ago: The 20 Minute Win. Barbara O'Neal argues that if you can carve out a twenty-minute window in which to write, and guard that twenty minutes against all intrusions, you can make substantial progress.
It's a great piece, and a great idea. I'm going to try the technique today.
How about you? Do you ever set a timer when you sit down to write?