Not for a minute. I've had this PowerBook for 51 months (according to coconutbattery) and I'm only considering upgrading this year. Technology's moving too fast for anyone to stay right on the forefront but a C2D MBP is as about as future-proof as you're gonna get.
In the way of Leopard, I've had every major version of OS X on this 1GHz machine and I'm sure it could handle Leopard, I'm going to get a MacBook instead. Hell, this baby even runs FCS pretty fast too.