I enjoy using my computer, especially at night when it's quiet. I enjoy it so much that I often forget to get up and stretch every few hours. I also stay up way too late. My propensity to get caught up in my Twitter stream or my RSS feed is one reason why I bought Coffee Break.
Coffee Break sits in your menu bar and forces you to take a break. You select the time you want to take a break and the app will darken your screen when it's time to walk away from the computer. There's a countdown timer that'll warn you when a break is about to start.
When your break is over, the screen will brighten, and you will be ready to roll back into what you were doing. If you're on the computer for an extended time, you can schedule several breaks throughout the day and add a reminder so you don't forget why you are breaking.
Coffee Break is a pleasure to use. It's visually appealing and easy to configure. The controls are intuitive and it's simple to turn a scheduled coffee break on or off as needed. It's also a lightweight app and hardly uses any system resources. It's one of my favorite little apps. Coffee break is available in the Mac App Store for US$2.99.