Carebears care! (and usually fail)

This is much more of a raid-leadership post than a guild-leadership post, but it needs to be said:
evaluating the raid team is essential to success.

OK, that isn't very clear; what I mean to say is: tell people about their mistakes, lack of gear, or lack of skill.
Sometimes there is a legit reason for somebody to be playing below their usual level: new spec? trying new gear? gem or glyph changes?  Sometimes people have bad nights with their ISP connection.  But in order for a player to be having a bad night, they need to have had a reliable string of good nights first.

Much more commonly, in my experience, is a new raider who is over his or her head.  They are missing gems or enchants, have a hodge-podge of gear, or have not raided with their class.  Maybe they are very used to PVP or soloing.  Maybe they got run-through some lower level content.  Maybe they are being asked to do something different (CC in the faction champions fight comes to mind).  All these things can lower their output.  Sometimes, they just don't know what to do.  The trick is to determine who you are dealing with.

A really good raider, a holy priest, changed from holy to disc for the Saurfang fight.  He seemed to be struggling a little bit.  My priest, Acquinas, has been disc forever, so after a few pulls, I looked at his spec and we made some adjustments.  After that, his output was awesome.  In the same raid (which was desperate for heals), a fellow guildie brought his resto druid, an alt.  The druid was not geared to this level.  I was astonished at his output, given his gear, but still, he was just not ready for the content.

In these two healer situations there is a clear analysis, and corrections; for the priest, fix the spec and rotation; for the druid - he's doing all the right things, but needed moar gearz.

It's not all bad news tho!  In this analysis, I love taking the opportunity to take some people who are doing great things and publicly congratulating them for being awesome.  "Dude, whatever your rotation is - you're kicking ass!"   "Holy cow! You are getting that CC off every time!  Awesome!"  "Hey guildies, if anybody wants to see somebody who knows his class, check this guy out!"

In any event, without adequate evaluation any raid team will not be as successful as they should be.  Everybody can be doing something better.  Progression typically demands it.