I've only used one at the flagship stores (too expensive/big), but the keyboard on it should be a benchmark for all of Nokia's other keyboards. It really is that nice.
When I was heavily interested in the N97, I was looking for it to be a replacement for an E90 I never owned, but it seems to be just the opposite. Having tried out a lot of hardware QWERTY's recently (N97, E71, Curve, Palm 755p, Palm Centro, E90, E75, G1, Sidekick 2009), the N97's ranks the lowest. It's not unusable, but it's close.