User groups really don't mean much on these phpBB setups. The most useful thing I've found them to do is you can make a "moderators" group and automatically give everyone in the group the mod powers. Could also be used to divide up the regular, most knowledgable posters here into areas of expertise. IE, "Drag racer group" "Puller group" "Boat group" "Builder group" etc etc so people could see who to direct questions to.