Never heard of it either. But some Googling returned a nice table with specs and some photo's : http://www.military.cz/usa/air/war/bomb ... b32_en.htm
Did flew couple of missions to Japan at the end of the war. Sakais last claim (last day of the war claimed in the book Samurai) was supposed to be B-32.
That's a pretty neat summary from what else I've read. An unremarkable aircraft whose production was delayed and decidedly inferior to the B-29. Completed as an insurance measure in case the B-29 proved unsatisfactory IIRC. As Tiso noted, they flew only a handful of missions and the only claim to fame of the type was that it was the last kill of Sakai (Although IIRC this actually occured after hostilities had ceased).
Here is some more info: http://www.daveswarbirds.com/usplanes/a ... minatr.htm and the omnipresent Wikipedia: http://en.wikipedia.org/wiki/B-32_Dominator It was common practice in the US prior to and during WWII to order a prime (the B-29 in this case) and a backup (the B-32). Usually the back up was the inferior plane. In one exception, the F4F Wildcat was the backup to the F2A Buffalo.
This is fairly standard, the RAF had 3 'V-bombers' in service because one (Valiant) was a more basic design intended as a fail-safe insurance choice should the more advanced Victor & Vculcan designs fail.