In my opinion: Not as much as some people think.
Two videos I'd like to use to highlight my point are these:
2v3 Arena - Warrior/Druid: Rating 1650-1900
Accompanying thread: http://forums.worldofwarcraft.com/thread.html?topicId=712008064&sid=1
2v2 Naked Arena - Hunter/Priest: Rating 1700-1800 http://files.filefront.com/WePlayNakedwmv/;8628918;/fileinfo.html
Accompanying thread: http://www.arenajunkies.com/showthread.php?t=929
Yes, they're old vids... but they still show that skilled players can climb their way up the Arena ranks whether they have good gear or not. They may not be able to hit 2000+, but they can definitely get a high enough rating for at least one piece of armour every couple of weeks... and really, that's all you need to catch up gear-wise.
If someone can do 2v2 naked against S2-geared people and get an Arena rating that in the current season would have been high enough for 4 pieces of Brutal Gladiator, I'm damn well not going to make any excuses for myself about being stuck in the 1600s due to sub-par gear! :P