I'm betting on WWDC 2012. I think these new MBPs need some work yet, with all the new technology, if being installed will be a challenge to make work. Usually MBPs are under-clocked to deal with things like heat. Plus I think Apple wants to raise their endurance value on the market for the MBP which gets updated quite often. I think they dislike people predicting their new models, because it reduces the value of the current model, but on the other hand does increase their public image.
WWDC 2012 is the best bet.
So if they are announced then.
When would they be shipping out? By end of June?