I think the old IBM keyboards are overrated, in general. People like what they originally learn on, and it's almost impossible to change that. The preference for the old AT keyboards came from 'old schoolers' who grew up on Selectrics and liked the similiar tactile feel.
My favorite keyboard was the LK201 that came with the old DEC VT220 & up terminals, and the Rainbow PC's. Smooth, low profile, spread out just right, with just enough throw, and quiet (but not silent). The closest I've come to that was Apple's Extended Keyboard II. I still have two around here somewhere, that I'd like to adapt for use on my Windows PC. Anyone know if there's an ADB-PS2 adapter out there?
For laptops, IBM keyboards rule. I'd take a clunky old Thinkpad with that great keyboard over any tiny new one. I'd be more productive on the older laptop in the long run.