How much does data weigh?

I subscribe to PC pro magazine (I'm a bit sad like that), even though these days a lot of what they talk about is over my head. Good editorials, incisive comment, and really good and valuable reviews and labs tests. I've made many purchase based on their review recommendations and "A List" picks, and never regretted any of them. I've also steered clear of stuff that I was going to buy on their say so.

Anyway, I was browsing their site today and came across this bizarre post about a question they'd received about the whether hard disks weigh more when they're full of data.

I'm not sure if it's a wind up - it's August after all, not April but it gets you thinking.

To my mind, a bit (or byte) of data is actually only a bunch of binary switches - on or off, or 0 or 1 if you like. Therefore whether on or off, 1 or 2 it doesn't weigh any more or less..........does it?