I have been pretty lucky so far. Most things have been full LS/FC parties, but there have been a couple of the later storyline fights that we had to DF for a few extras. Thankfully, they were all pretty understanding. Had no problems with us watching cutscenes, and didn't complain when we screwed up, they even gave advice in a friendly manner.

My roommate, on the other hand, has had some pretty hellacious DF encounters; people throwing fits and dropping, blaming others for their mistakes, being verbally abusive towards others, etc.