How To Downgrade iOS 5 to 4.3.X
Now that iOS 5 has been released a lot of people including myself have updated their devices. Without first taking notice that some Cydia apps, tweaks, themes might not be working, the jailbreak is tethered, etc. But there is a way to downgrade and it can be done in a few minutes. For this to work you must have previously backed up SHSH blobs for the iOS you want to downgrade to. I recommend downgrading to 4.3.3 for the simple reason that you can jailbreak with JailbreakMe.
You can grab the firmware fileyou want to downgrade to from here
1. Download the firmware you want to downgrade your device to.
2. Now put your device in DFU mode. To do this, turn your device completely off, press and hold the Power and Home buttons for 10 seconds, then release the Power button but keep holding the Home button for 10 more seconds. You should see a blank screen, if not, try again.
3. This will trick iTunes into accepting an old firmware by preventing it from connecting to Apple’s servers: Go to C:\Windows\System32\drivers\etc\ and open a file called "hosts" with Notepad.
4. Add this line of text shown below to the end of the hosts file:
5. Now launch iTunes, select your device and hold "Shift" on the keyboard and click on "Restore" and select the desired firmware.
If you get the iTunes logo download TinyUmbrella for Windows or Mac. Launch it and select "Exit Recovery".