To many you're a hero. (Although I could never make the time for all 3.)
To be honest, it is a huge waste of money and space. I basically use my Wii regularly for Wii Fit, and that's pretty much it. The 360 gets used steady and the PS3 gets used not nearly enough to justify the money I spent on it. I'm hoping God of War 3 and Uncharted 2 will correct that. Everyone has the one system that has the majority of the games they want to play, or one that most of their friends have. The smartest bet is just to go by one of those two things. You can borrow games and you'll have people to play with online.
I could easily find other ways to exercise than Wii Fit, though I do like the package and it made exercising a bit fun again. The PS3 was the last one I bought, and all my friends have the 360, so it really isn't a draw for me. I do prefer the game selection on 360, and I prefer Live over PSN despite the price, but if all my friends had the PS3, I'd probably use it more than my 360. I tend to buy multiplatform titles for 360 just because that's the version my friends have for online play.
There really isn't a compelling reason to buy both the 360 and PS3. One friend of mine really wants to play a few PS3 games, so I just told him he could borrow mine since I don't use it much. He already has a 360 and there are only a few exclusives he wants to play. Between the cost of the PS3, taxes, peripherals and games I could be saving him as much as $1000. The same would be true for 360. These things aren't cheap, so owning two is just stupid.