Cal Newport experiments with a day of forced focus:

Here are the rules: All work must be done in blocks of at least 30 minutes. If I start editing a paper, for example, I have to spend at least 30 minutes editing. If I need to complete a small task, like handing in a form, I have to spend at least 30 minutes doing small tasks.

Taking the rigid, batched schedule to an extreme, with interesting results. Cal also writes the excellent Study Hacks blog.