ExpandProbably doesn't need saying, but the machines are out if you're particular about your bevel angles, or if your knives are ground asymmetrically (most everything from Japan). You can certainly sharpen an asymmetrically beveled knife in one of these machines, but you'll end up with 50/50 bevels on a knife that's designed otherwise, and you'll have funky edge geometry that won't perform so well.
I agree that the machines with little wheels are out for thinning. But a decent belt machine setup will do the job.
I have one of these, from my dad's packing plant: http://www.kasco.com/hook-eye-sharpeners.html
A Burr King and a glass platen would be better, but you can have a pro do a lot of thinning for $2K.