According to
http://bitcoin.sipa.be/, it seems some big miners will purposely slow down the hashing just before the difficulty adjusting to reduce the jump? Although I know that does not make much sense, since what they get is based on their hash rate percentage, not the difficulty. Maybe they are just doing that to save the environment.
I'm seeing the opposite on that graph. Looks like the difficulty growth levels out for a day or so after each adjustment. That would be consistent with people looking at their mining revenue after an adjustment and deciding to shut down their rigs.