From everything I have read, you can usually expect the belt to be in good/great shape. However, the notorious area of concern is the water pump leaking over time onto the belt causing wear and the potential for failure.
I'm sort of in the same boat as everyone else, 400ish hours and I don't think its ever been done, but its certainly not something I'm really looking forward to tackling if it isn't "necessary".
But, a 20 year old water pump makes me a bit nervous.