Had a dabble running a YouTube campaign in April this year. Ran the campaign for a month, had 32,483 impressions, 1,314 views, which gave a view rate of 4.05% (no idea if that is good or bad!).
Spent £108 over a month, but couldn't track any direct results back to the campaign. It was more of an experiment having never really done anything with YouTube before.
I'd consider it again but with better tracking in place.