I've swung wildly between the "Oh god, dice will totally screw with my immersion by making my character change their mind due to a crappy pose and good dice" side of things and the "Oh god, why must everyone pose like they're perfect liars and perfectly charming we need a damned social combat system" side of things during my time MU*ing.
The system I've been designing currently has a "hard" social combat system (based on a simplified version of A Song of Ice and Fire's system), but I do have cut-outs--winning social combat gets you toward your goal, it doesn't necessarily get you all the way there (physical combat is the same way in that you generally have to keep attacking after someone has fallen to actually kill them), and you can always walk out, although that may very well have social consequences as well.
I don't think there is a "base" way to handle social dynamics--I certainly don't want people acting as @SG described (posing in such a way that does not back up their stats), but I also feel that a badly-written pose punching someone with a ton of successes behind it is a lot easier to roll with than a badly-written pose convincing or seducing someone with a ton of successes behind it.