How often do you revise your resume? I used to fill in updates every year or so early in my career, but I've been slacking in the past few years and only update it when I am searching for a job.

I decided tonight that I would give it an update with my most recent job even though I'm not looking for work... its only been a few months since I quit and I've already forgotten about half of what I used to be responsible for!

How often do you work on revising/updating your resume? Is it ready to go at a moment's notice?