How Often Do You Clean Your Laptop?

I feel embarrassed right now. For the first time in ages, I actually paid attention to the keys on which I'm typing. And they're filthy. I am a bad person.

In fact, I don't think I've cleaned this Macbook Air since I bought it about 18 months ago. That's an awful lot of dirt and grime to have built up. But I can't be the exception, right? So how often do you clean your laptop? Or are you filthier than me?

Image by joeymanley under Creative Commons license