One of the big issues that I've seen with forcing role-playing for social skills is that, as I'm sure many of you have noticed, many people playing these games don't possess these social skills, especially in the same capacity of their characters.
My paladin currently has like +11 to diplomacy, I can say with certainty that he is much more sociable than I am and would be much more articulate in how he talks to npcs than I would be. The roll is to represent how well he did at social interaction, not how well I did.
The same should absolutely be true for intimidating someone to alter their attitude towards you.
I won't speak for other GMs here, but in home games and in public games for PFS, I don't let people generally just make Diplomacy or Intimidate checks without, at the very least, telling me or describing to me what they are attempting to do. I understand that some people may be shy, or not speak well or eloquently or whatever - I won't penalize a person for that. But, I will require a player to do more than tell me "I am making a Diplomacy check." That won't cut it in my game.
And, if what they describe (or if they are good at role-playing and play it well) is particularly creative, novel, etc., I'll likely give them a +2 bonus to boot.
Personally I've always found it interesting that -
"I roll disable device to pick the lock" is usually prefectly acceptable
"I roll diplomacy to change attitude" is not
I've always thought that the best response to a high diplomacy roll is simply 'Ok, they are friendly, now what are you trying to get them to do?'
And for the record I fully support the idea that diplomacy/intimidate/bluff not be used to wreck modules and be used like dominate or charm. A guard will not leave his post because he likes you, and you can't convince someone that a tree is made of cheese.