If it was cold at the time (below 50 degrees F), you probably experienced carburetor icing. I've usually had to keep blipping the throttle for as long as 30 seconds before my bike would idle.
It's most likely to happen after riding at speed for more than 5 minutes. The first time you come to a stop it won't idle until some engine heat makes its way back to the carburetors.
My personal solution to the problem is to not ride in the cold. Basically that means waiting until the afternoon rather than riding in the morning during the winter. If I find some reason to ride anyway in the cold, I just remember to help the engine out a little when I come to the first stop after riding a ways.
I've had this issue on my S4 after riding for a while, then stopping. It was pretty much a hot weather thing. I would go to start her back up and she wouldn't run w/o the throttle advance lever pulled on. It would take a few minutes for it to get back to a smooth idle.