I have discovered something quite cool on GNOME. You can set your system to make you take breaks.

To setup: Computer->Desktop Preferences->Keyboard->Typing Break

Although designed to combat RSI, this is also good for your eyes. It is a good reminder for those of you who get sucked in for hours at a time, to look outside, to get something to eat or drink, to go to the loo.

A little bar in your notifications panel will show the bar fill up over your set working period, then it will start flashing red when it's about to make you break.

There is an option to postpone your break, which can be useful if you're in the middle of something. Like writing this blog entry!

Note that this just xlocks. You can still switch to a TTY.