A couple things

I'm going to cover a couple things really quick.

Baradin Warden's Rep

At Mr. Popularity (Rank 2) or Guild Level 12, you receive an additional 10% reputation reward for killing monsters and completing quests.  That means that if you complete the 12 daily quests available through Tol Barad, 6 on the Peninsula and 6 on the Baradin Hold Island, you will get a total of  4050 reputation.  That means over the course of three days, you can move through the entirety of Revered. 

Matchmaking Value and Rating

 "If you win, Blizzard will drag your rating up to your Matchmaking Value.  If you lose, Blizzard will drag your Matchmaking Value to your Rating."  This is the simplest way I've been able to describe the system between Matchmaking Value and actual team Rating.  Your rating is what matters, it's what you get achievements from and allows you to access higher levels of gear.  Your matchmaking value is what allows you to ascend ratings faster or slower; if you beat teams at a higher matchmaking value, then your matchmaking value will rise and your rating will try to rise with it.

Recount

Recount is the only addon that I ever recommend to other players.  It is the quickest and best way to gauge how you are performing.  Let's say the following:

You are doing a boss fight in a dungeon with guild mates.  You are spec A.  You wipe on the boss fight.  Your Recount informs you that you did DPS-A.  After the wipe, your guild mate asks you to switch specs.  You are now spec B.  You wipe on the second attempt.  Your Recount informs you that you did DPS-B.

So, now you compare your Recounts.

On Damage Dealt, DPS-A was higher than DPS-B.  On Damage received, DPS-A took more damage than DPS-B.  On Interrupts, DPS-B was higher than DPS-A.  What does this tell us?

It tells us that DPS-B was able to take less damage likely due to the increased number of interrupts over DPS-A.  If another person were able to pick up on the interrupts, then you should respec back from DPS-B to DPS-A for the higher numbers.

So, that's a highly controlled situation but it covers why I love Recount.