Anecdote from one of my campaigns in recent years, (I was DM):
The party had just traveled to a city and were headed in through one of the gates. The city was essentially Lawful Evil, and was in the middle of a "difficult situation," so the gate guards were attentive and a bit strict. This was all part of the adventure plot the party was coming into.
The guards were giving everyone a thorough check before letting anyone come and go through their gate. I didn't intend this "encounter" to play out as anything more than just a demonstration of the tension of the city.
Now, one of the party was a "dervish"-style knife-fighter, with robes over his chainmail, and a wrap around his face and head. I knew this was the character's look, as we were about two dozen game sessions into the campaign. As far as I knew, this was just a look/dress style thing, nothing more.
When the gate guards told the fighter to show his face before entering the city, the fighter refused. Turns out, the face wrap was a religious thing, and he couldn't show his face to infidels. I, as the DM, didn't know this, and the other Players didn't know this. <sigh>
Now, as I'm sure many of you have already thought of, there are many ways of overcoming this encounter. Social skills, bribery, magic, finding another way into the city, etc. What did the party come up with? The masked fighter opted to just camp outside of the city while the rest of the party went in.
Holy crap! So that Player ended up basically sitting out part of the adventure, (most of a whole game session), because we played through an encounter with the city guards.
So, although I like playing out a "non-exciting" scene if it sets a mood or sets up an adventure, but this kind of thing teaches me that every such scene gives the Players a chance to totally screw up an adventure. I've also seen adventures break down based on the initial role play encounter with the quest giver. If the DM doesn't play the NPC just right, someone takes offense or gives offense and the whole thing falls apart.
Also, from what I've seen, the people who most like to play through the "non-exciting" scenes tend to be the ones most likely to skew that scene into more problem than it was intended to be. They stretch what could have been a 5-minute encounter out to an hour-long drama that cripples the rest of the game session.
Bullgrit