I've got one, which I got back in 2004.
I'm running Leopard on it these days, but only really use it as a laptop now (I was using it as a Desktop replacement for a couple of years). Certainly not as quick as it used to be anymore.
My biggest issue with the machine is that when Tiger was released, upgrading to it caused one of the memory slots inside the machine to die. So if you had RAM in both slots, you lost half of it. Apple did run a free repair service for this, as it involves replacing the motherboard inside it, however much to the annoyance of many people it was on a very small serial number range.
There is still an attempt at a class action lawsuit against Apple, not really sure what is happening with that anymore. Pretty annoying really.