The Dev-Team has updated redsn0w to version 09.8b3 with support for the latest release of iOS. The 4.3.4 firmware does not add new features to devices, and exists solely to patch the PDF vulnerability used to exploit the operating system. If you decided to ignore all the warnings and upgrade anyway, you can still have a tethered jailbreak—unless you own an iPad 2. Mac users can check out the recently updated PwnageTool.
Update #3: For the convenience of kernel hackers like @comex and @i0n1c, we have a new redsn0w 0.9.8b3 that supports a TETHERED jailbreak for iOS 4.3.4 on all devices that have 4.3.4 except the iPad2. The vast majority of people will want to stay back at 4.3.3 because that’s where the untethered jailbreak is! There are no new features in 4.3.4 — only fixes for jailbreak exploits.