Mpc1kallday wrote:anyone wanna explain more in laims terms what it does>? 
If you mean SIMULT, it just makes one pad trigger another pad. So, if you want to have two snares layered in your sequence (for example), you don't have to program in 2 snares everytime. You just assign each snare to its own pad, but make one of the pads trigger the other pad with SIMULT.
The reason it's dope, is because you can still edit the envelope/effects for each pad independently. So you could have no reverb on one snare (again still going with the 2 snares example), and lots of reverb on the other. Or a tight decay on 1 snare and none on the other (this is handy if you are chopping hits that already have reverb from the record you sampled but you don't want to hear 2 sets of reverb).Etc.
The JJ SIMULT looks even better than the old one, because it looks like you can assign 4 pads to be triggered by one pad (previously only 2 were possible on the MPC2000/3000). I've been holding off on getting the JJ OS, about to install it now! Whoot.