I use tire warmers all the time. But I use it as a mental thing (no not you Layne, thats gross). I feel that if I can get out there and chuck it in right off the bat I will not be "trained" to take it easy.
When I was racing full time I rarely practiced either for the same reason. I would show up for Friday practice and do three 5 lap stints to scrub in 3 sets of tires. Then I would park the bike and go get dinner, hotel, movie, etc. The next morning I would show up at the track late and skip practice. My first lap of the day was my warm up lap, which I would run at about 95%. It worked for me. Some of my fastest laps of my life were the first two of a race.