We are about a week away from seeing if NI's Bandstand is the do-all GM program we've been wanting. There's several programs that can play GM SMF's, like Colossus and Reason (with the Omnisounds GM soundset) but none of them accept GM patch changes so they aren't quite ready for stage use without going to a lot of trouble. There's also soundfonts like AJ uses, but the holy grail is to find a great sample-based GM-compatible program and Bandstand has that potential, on paper anyway. Bandstand will be released November 7th.

BTW: I have to say that not all of Native Instrument's products are perfected - I've been hearing from some people who are very unhappy with NI's Akoustic Piano program so we can't take anything on faith.