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You can turn it off, just click on the pencil icon in the settings: http://i.imgur.com/EbxExC3.png

Yes, Google rolled out this update globally (which is rare for them to do. I think this is the first time they have done it on a big algo update, but I might be wrong on this one). Source: http://googlewebmastercentral.blogspot.com/2012/04/another-step-to-reward-high-quality.html

I have used disallow parameters for all kinds of things; you can set it up and test it in Webmaster tools under "crawler access" before you implement on your site to confirm it's done properly.  There have been a few times I've had to tweak it to get exactly what I wanted. I'd test with the "/" in front of it as one option - again, just in testing, to see if there's any difference in results. Since Google already got a hold of it, it'll take a lot of time to see results but don't be discouraged since they have to re-crawl and figure it out. Good luck