Average Lifespan

Being a 'switcher' as of late last year, I was wondering what the average time a mac owner kept their systems. It seems to me that Apple's product lifecycle is much greater than that of most PC manufacturers. I am approaching the one year mark on this iBook and it still never ceases to amaze me. I also own a Dell that is roughly the same age and in the PC world it is a dinosaur!

I've had mine for almost 4 years now and since it's a laptop, the only reason that I am updating is because the hard drive is too small now, but the speed is still great and I love using it So average.. I could see as long as 7 years, but probably 5 years is average.