if everone is that strong roles aren't all that worthwhile unless you're racing a stage race. I ride with a club that routinely controls the cat 3 and 4 races in the area. We define loose roles at every race, though it basically comes to down to finishers and 'workers.' Workers then usually split themselves up again, guys who work the first half and guys who work the second. We usually have the weaker guys (mind you guys understand who is stronger and who isn't, we don't just tell someone they suck) work the first half, attacking and covering attacks, maybe send one of our strong guys out on an early break depending on the field. The stronger guys generally work the second half, again doing the same thing, though they also will make up the leadout train if needed, these guys generally can finish a race if needed, its usally just the finish isnt optimal for their riding (say myself in a flat field sprint). Then we have finishers, who generally get free reign, depending on the squad there might be none or once we had three (stage race), they might be waiting for a sprint or for the right moment to attack the field, but when they go, the team does its damnest to make sure that guy wins.
But none of its cemented, things are fluid and we communicate a lot, so if someones feeling good or bad it gets taken into account. We also talk with other teams to get breaks to work, and always *always* attack the hell out of the field.