Stratasys has released a video detailing some of their secret (well, maybe not so secret) finishing processes. The video shows various tumbling media machines that operate similar to rock polishing tumblers - an object is tossed around within a bath of rough media. Gradually the objects become smooth after a relatively short period in the tumbler.
What's interesting for home 3D printer operators is the explanation of the different types of tumbling media used at Stratasys. Through extensive experimentation Stratasys has determined the best type of media for different 3D printed plastics.
This approach could easily be replicated by hobbyists using much smaller tumblers, if similar tumbling media could be obtained. We took a quick look and found sources for said media, but the minimum order was 800 pounds. Anyone need any?