The iPhone Dev-Team has released RedSn0w 0.9.8b3 which can perform a tethered jailbreak on iOS 4.3.4.
Since this is not an untethered jailbreak and will not work for the iPad 2, we recommend jailbreakers to stay at iOS 4.3.3 and wait for untethered jailbreak for iOS 4.3.4.
iPad 2 jailbreakers should definitely stay at iOS 4.3.3, since JailbreakMe is currently the only jailbreak for the device and will not work past iOS 4.3.3.
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.