word!
I'd never go down on a guy unless i was 110% ready to give it everything I have. Thankfully its something I enjoy doing and take very much pride in pleasing him to his fullest.
I'll stay there for an hour if he desires...
but verbal communication is the key. I ask him what he likes, if he likes what im doing and what it is he wants me to do. With out the verbal, its just one big guessing game... and most are reluctant to request what they want or say that they don't like something.