I had heated grips on my previous bike, haven't bothered to put them on my current one. I will say that the combination of heated gloves and heated grips was pretty awesome when the temps dipped under about 20 degrees!

I think the key to cold weather riding is wind protection. The Effective Wind Chill at 15 degrees and 70 mph is a number I don't care to contemplate, but is perfectly liveable with the right gear.