The Warsong will continually increase its effect, probably each week. Eventually, when you step into the Icecrown Citadel, you're going to be rocking a 30% bonus to your damage and healing, as well as your tank's health. While I'm not sure a mere 30% is going to render the complicated dance steps of the Icecrown bosses completely inconsequential, this buff is going to go a long way towards creating an "accident buffer." If your raid doesn't quite sidestep out of fire fast enough, for example, they won't instantly be burned to a crisp.
The other affect the Warsong will have is to make incremental increases in gear more effective, while still making the daily Emblem of Frost march a little less mandatory. A weekly 5% increase in damage is beyond any buff a piece of gear can provide. (At least, any single piece of gear.) As Brian pointed out last month in Scattered Shots, gear just isn't the universal fulcrum of performance improvements. Raid buffs and skill are the most effective means of "getting the most" out of your character.
If you've already "maxed out" your raid composition and each one of your raiders' skill, drops aren't going to radically change the way your raid performs. (Of course, I'd argue that if your raid composition and raider skill are already that high, you've probably cleared through available content without the Warsong.) Relying on gear improvements to get your raid a little further isn't going to get you anywhere.
In terms of that, a 5% to 30% jump is going to be pretty darn meaningful. This means incremental increases in gear aren't quite as mandatory to your raid's improvement, since bosses aren't getting tougher while the Warsong keeps on stacking up. It does mean that every gear increase will be that much more awesome, though.
Let's say you need 10,000 raid damage per second to kill the FailBoss. The FailBoss encounter is a pretty straightforward fight, and everyone gets to hold still, ignore gimmicks, and spam their buttons as fast a tilty bird will let them. It's Patchwork all over again. Say your raid is only doing 9k DPS, however. You're a 1,000 DPS short of killing FailBoss.
If an item drops from another instance that increases your DPS by 200, you're still 800 DPS shy of slaughtering this guy. (After all, 9k + 200 = 9,200.) However, if you do pick up that item and you're under the effect of a mere 30% Warsong, that 200DPS is actually worth 260 DPS. Before, you needed 5 200DPS increases, but now you merely need 4 similar items.
Most real world examples aren't going to be that cut and dried, of course. But the Warsong will be a snowball rolling down a mountain, picking up momentum and snow as it goes. The buff will help guilds get more gear faster, and it will continually build on its affect as time goes by. Even more importantly, if your guild has a limited raiding schedule, then it will allow you to get through the bosses faster, and make better use of your time. For everyone who isn't particularly hung up on the pride of saying "we did it without the buff."
But what if you are one of those folks who want to be on the bleeding edge? The first thing you're going to have to do is take a hard look at your own raid, and gauge how you're doing. If you're on Arthas -- or very near to him -- then maybe this buff isn't going to be necessary for you. After all, you're pretty much done the normal mode content already. (If you're doing Hard Modes, chances are you have already made your decision about whether or not to use the Warsong.)
But if you're one of the many guilds struggling at Rotface, Putricide, or the Crimson Halls, ask yourself if a single week of Warsong-boost wouldn't help. Do the dance with the buff, get the fights down, and maybe pick up the extra loot. Then go back and try it without the buff. If having the Warsong -- and thus that accident buffer -- might help you learn, take the opportunity to learn. Not to be all Marcellus Wallace about this, but skipping out on an opportunity because of pride is a bad idea. Any sharp tinge of guilt because of the 5% buff is just pride messing with you. Ignore it. Take the chance to get better, learn the fights. And then, once you're through, if you still want to say "We cleared all this without the buff" -- do it, now that you have a grip on the fight.
I feel like I should close with some "that's how Sue sees it" line or something here, but I want to stress to all the people struggling about whether they want to use the buff that there's no reason to ignore it except for the pride. Blizzard put it there to make Icecrown a little more accessible. A lot of the folks who blew through the content early are absolutely amazing players who've spent years honing their technique. (And, since the patch, many of them have spent every day collecting Emblems of Frost.) Not all of us have that time.
Take the buff, run with it, and blow Arthas back to his daddy. Good hunting out there!
Edit: I made a napkin-math error in the example, which I've now edited to make my example more clear.
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