I've modded my own Record Power belt sander for sharpening duty but I've also used one of these if anyones in the market for a sharpening system:
Bit pricey but well made. The only slight niggle is that belt changing could be much quicker and easier and if I were designing one from scratch I might make the platen and belt a bit longer. Overall though, very useful.
I wonder if the far east will start making these at some point - maybe an opportunity for some one on here ...