It kind of drives me insane (yes, amazingly, I have more insane to be driven to) that at times, raid progress is stalled not by a lack of capable raiders, but rather by the design of raid encounters that punishes them for the type of DPSers they are. As a raid leader, I am not a big fan of telling capable players to switch from enhancement (a spec they may be skilled at) to elemental (a spec they may not have any experience with) because even if their DPS drops, it will be better for the raid and our healers to have them out at range -- just one potential example. Worse than telling people to switch roles is telling them you need them to step out for another player because they simply can't switch to a non-melee role.
Painting a broader picture
When I see a talented and skilled paladin tank powerleveling a druid because he can be a moonkin (and thus fulfill a ranged role) as well as heal or tank, it drives the point home to me. As much as we're always told that it's dangerous to use what happens in our personal gameplay to paint a broader picture of what's happening in the game entire, I can't help but wonder how many other raids are having this experience. It seems to me a failure of design that the raids themselves provide selection pressure to try and force my players into classes they don't want to play. If I'm intended to bring my friends because they're good players, why should my friends and good players be forced to roll classes they don't want to play?
We already have to divide raids into tanks, healers and DPSers. A further division of labor in the DPS ranks, especially when we're supposedly to be able to raid in either 10- or 25-man format, really makes things unnecessarily convoluted for no good reason. Fights designed to be punishing because you're standing too close or too far away from something need to be balanced out so that raids don't need to cherry-pick their roster to succeed (or at the very least, so they won't suffer unduly). This should go for ranged players as well; it should be just as viable to field an all-caster or all-ranged DPS squad. Right now, the all ranged squad is absolutely viable: there is no penalty associated with having an all ranged raid. Try an all melee and see what your healers say.
We've got more raids on the way, so please, let's see some flexibility in who you can bring.
World of Warcraft: Cataclysm has destroyed Azeroth as we know it; nothing is the same! In WoW Insider's Guide to Cataclysm, you can find out everything you need to know about WoW's third expansion, from leveling up a new goblin or worgen to breaking news and strategies on endgame play.