Isn't it possible to cause a significant inflation in the arena system by consequently buying new teams and quickly driving them to ~1300 rating, over and over?
Let's say for example that you are willing the put 2000g into this.. that's 10 5v5 teams.. that's about 2000 rating distributed among the teams around 1500-1400. This introduced rating amount will propagate through the system and generally raise the rating of all teams in the 5v5 pool. This in turn will make it easier for you to gain rating.

I'm not going to try this, and I don't advice anyone to do so either.. since it's in a gray area of what's allowed in the game. However I find the concept a little interesting and amusing. It also highlights one of the biggest design flaws in the WoW arena system - your rating can be reset by creating a new team.

I'm entirely convinced that it works though... there aren't that many people out there playing 5v5, and even fewer are creating new teams.. so every added team to the pool will have a significant impact.