pdzoch
Explorer
Group checks are for when a number of individuals are trying to accomplish something as a group, so it would require a fictional action declaration along those lines. I'm not a math guy, but the rules say "in such a situation, the characters who are skilled at a particular task help cover those who aren't," so the intent appears to be that a group check would not be a penalty. Someone smarter than me will have to say whether the math supports that intent. My experience at the table says that it does since you mitigate the risk of that one guy failing the check and blowing it for everyone else at the table.
I recall an adventure a few years in Dungeon magazine that had a masquerade ball event where the characters had to impersonate a person of high class, gather information discreetly, and and blend in without being discovered as a fake. Charisma based skill checked were heavily employed. DM notes included, if I recall correctly, whether or not a failed charisma skill check would expose fellow adventurers. At first, a failed check resulted in an unsuccessful influence of a guest, but repeated failures made each check harder as the poor reputation/popularity spread. If the player characters were seen associating with one of their failing player characters, their subsequent charisma based skill check became harder also. Likewise, successful checks with higher charisma persons enabled the follow-on checks to be easier.
While some do not like the masquerade ball events in a D&D game, I thought charisma based checks made lots of sense here, and I really liked the "guilty by association" penalty employed in the popularity contest to gain information.