I've been looking into three-button mice over the past few days. 
Unfortunately, most of the ones listed in the "Working hardware" list
(http://www.macbsd.com/macbsd/macbsd-docs/info) seem to be discontinued,
or at least the manufacturers no longer list them on website (this
includes Mouseworks, the logitech, and animax listings).

The only one I could find still being made was a three-button model by
MicroSpeed (m/n# MD-300).  Touching base with the gentleman whose name
appeared in the listing (Brad Salai) -- that was apparently under NetBSD
1.2 and "only the first button ever really worked properly".

Has anyone tried one of these out?

Reading through John Witkoski's HWDirect kernel info, it looks
encouraging.  (Thanks John!)

Is there any kind of general consensus about 2-button mice? (Now why the
heck are there so many of those?).

TIA

Steve Revilak