I absolutely agree with the issues about communication. The biggest difference I've seen between my guild raids, and pickup raids is the quality both of the leadership at communicating what's to be done, and the members at understanding how to follow instructions (ok, and general clue, but that's another issue!).
I've always hated the "follow me!" kind of leadership. It's a disaster waiting to happen. Leaders tend to forget that they don't have a huge glowing beacon on them allowing everyone to see them in the crowd. Add in lag issues, and it's ludicrously easy to get half your raid force running in the wrong direction.
Unless you are raiding with a force that you *know* knows the area like the back of their hands (and that pretty much happens exclusively with guild raiding, and is guaranteed to happen since you tend to raid the same places over and over and over), you have to assume that no one in the raid force has a clue where you are going, or what you are fighting. I've seen far to many raidleaders obsess over little details like who's responsible for buffing which groups, and spend no effort at all informing the raid group about how they are going to get to the mob and how they are going to kill the mob.
Beyond the communnication issue, Cal's pretty much hit all the major points. I'll even shorten the list down a bit by saying that there are usually two reasons a raid wipes (beyond stupid stuff like bad communication):
1. Bad plan. Cal went into much more detail (defensive use of CC/healers rather then relying on tanks, and setting up who'll deal with what when, etc...), but you can still boil it town to planning. You pulled the mobs in the wrong order. You fought them in the wrong spot. You set the wrong CH rate. You didn't have the right patchers ready to go. You didn't know about or deal properly with spawns during the fight. The reasons are numerous. The good thing about wiping this way is that usually your raid force arrives at their bind point thinking: "Ah hah! I see what we did wrong that time. Let's get back and try this other thing...".
Bad plans turn into good plans. After all, someone had to come up with the raid strat that most folks just read about on the net somewhere. Usually, you don't feel to bad about losing this way, since you know you've learned something about the encounter.
2. Just not enough force. This one hurts. Really. When you look at the encounter, and you know you are doing it the most effectively that you possibly can, but you just don't have the numbers or combination needed to win. Sometimes, it's just a single raid issue. You didn't have the turnout you wanted, and now you know what you'll need for next time. Sometimes though, it can be very demoralizing to a guild to fail this way. You know that there's nothing immediate that you can do to fix it. Having too many of this type of failure can be disasterous to a guild btw.
The good part is that, at least for those of us in more mid leveled raid guilds, this type of thing is the yardstick by which you measure progress. 6 months ago, maybe there was an encounter that you did as right as possible, but just couldn't ever quite beat. Today, after gaining more AAs/levels for your members, maybe gaining a number of new folks, and presumbably gearing up a bit, you can walk through it without hardly breaking a sweat. What starts out as one of the most demoralizing failure turns into a real sense of accomishment. There are very few long term raid guilds that can't look back and say "Remember, when <X> seemed impossible? And today, we do that as a warmup before heading off to our *real* raid objective...". It's a good feeling.