Setting a timer is good for focusing on a task, but you need to have a solid idea on what to work on. Assuming you have a goal, the next task becomes planning if you don't have a concrete next task yet. The five minute breaks are tricky though. I can't use them for browsing the web, since once I start that, I won't stop that after just the five minutes. Stepping away from the computer to spend some time thinking about what to do next would be good though. Not stepping away from the computer for the break and having the break stretch on is generally what breaks a Pomodoro run for me.

I should try the Pomodoro routine again, I've been a lot less structured with my work/break schedule.