A few words on the recent iOS 4.3 release

1. Pre-A5 devices already have a tethered JB with redsn0w 0.96rc8 custom bundle in the latest versions of PwnageTool/Sn0wBreeze. A5 Devices will have to wait till another injection vector to be found in the bootrom or userland. 
2. New kernel breaks MobileSubstrate, and as a result a large majority of Cydia packages that depend on the former. Saurik cannot be reached for comment but it is understood that a compatible revision could take some time. Saurik is working on a compatible build right now with a new and improved version of Cydia!
3. APPL's server is no longer signing 4.2.1 firmware, it is simply too late.
4. Downgrade to 4.2.1 using cached TSS blobs will result in a 1013 error due to a mismatch in baseband version. Simply jailbreak again with Greenpois0n RC5 or later to get going, notice that the "auto-reboot" command will no longer kick you out of recovery loop, TinyUmbrella uses the same command and hence no longer works. 
5. Multi-touch gestures is said to have been taken away in the final 4.3 firmware however it could not have been simpler to have it re-enabled. In \Applications\Preferences.app\General.plist search for "Mutltitasking"[sic], replace them with the correctly spelling "Multitasking" and you are all set. Seems like the engineers got incredibly lazy that they did not even bother to remove the code...

Update: Apparently jailbreak is not necessary, you can edit the said file in an iTunes backup and restore to get the same effect.