Janus,
I've got one section 8 tennant in Arlington. Single mom, kids and her family lives down the block. So far she has been an ideal tennat, and is genuinly grateful for having a chance to live in a nice neighborhood with good schools. Had I not met her and her kids, as well as her parents down the street, I would certainly have second guessed things.
For MA section 8 info go to:
http://www.massresources.org/pages.cfm?contentID=3&pageID=2&subpages=yes&dynamicID=753#rent
somwhere in there is a link to the 2005 HUD rents for a variety of units (2Br, 3BR etc) An initial inspection of the unit is required (a no brainer) as well as a yearly inspection. Tennants are on 1 year leases. At the end of a year your free to show them the door or renew. (rental increases must be approved by the section 8 authority however)
For me, it has worked well. An entire unit of section 8, I would probably rethink things pretty closely.
As an aside, know a good real estate attorney in MA to take care of some LLC work?