Lots of people here (NorCal) use trainer or rollers for crit/road race warmup. I've seen people warming up on trainers or rollers for hillclimb road races. Usually the short ones, but I've seen guys on trianers/rollers before stages of the Everest Challenge (the stages are 5-7 hours for the faster riders). If you warm up well on a trainer or rollers it's awfully conveinent.

I warm up really poorly on a trainer so I have to find a road instead. I've always been able to find something, but sometimes it's not very good. There's an increased risk of a last minute flat when you warm up on the road. If it's cold out you will be warmer on a trainer.

Don't worry about what other people think. Do what works for you.