How to downgrade from iOS 6 to iOS 5.1.1? I made a huge mistake of upgrading to iOS 6 today. I hate the release and I want OUT. When I try to downgrade by restoring to IPSW for 5.1.1 it tells me that the device isn't eligible for the build. What do I have to do to make iTunes accept this IPSW file and run the install?

You can read how to downgrade to iOS 5.1.1 on my blog : http://antonpug.com/blog
I just read this blog post and it looks like it's possible to downgrade but only if you do it quickly. Soon there will be no turning back.

Also, it's device dependent, as explained in this post

It worked for me to restore an old back up.