Living in MInnesota I've had heated grips on my last several bikes. Foam grips worked well but it took a while to notice the heat compared to others.
I use the Kimpex foil heaters sold by Dennis Kirk in the Snowmobile catalog at <
www.denniskirk.com> for about $25. They have a low and high position and I've never felt the need for high heat except to get them up to temperature. Otherwise low works well down to about 30 degrees for me.
I would recommend some sort of glue when putting the grips on -- I used hair spray -- it gives you a minute ot two to get the grips in place before it sets up. I let them dry overnight just to be sure. Never had a problem after that.
My favorite grip is the Sun-Line Grand Touring grips -- they're barrel shaped and of very tacky rubber that doesn't get slippery even when wet.
While they seem hard, they do absorb vibration and road shock well.