The new redsn0w works with all 4.3.1 devices excluding the iPad 2. Remember that it is likely that the download will be slow, or that it may knock out the server due to the high demand that these programs create. If it doesn’t work out the first time, try again or wait for a mirror. Be cautious of any unofficial mirrors that may popup.
Users who have already jailbroken 4.3.1 with sn0wbreeze can run the updated redsn0w over it without a restore.
WARNING WARNING — ultrasn0w users don’t update yet! We need to first release an update to ultrasn0w that fixes some incompatibilities when FW 4.3.1 is used on the older basebands supported by ultrasn0w. And remember once we do fix ultrasn0w for 4.3.1 (we’ll announce it here and on twitter), you must only get there via a custom IPSW from PwnageTool, Sn0wbreeze or xpwn! Don’t ever try to restore or update to a stock IPSW, or you’ll lose the unlock!
Let us know how it goes in the comments!