If you update to the latest firmware 4.2.10/4.3.5 you'll have to perform a tethered jailbreak. Which blows. The only difference from that you'll basically have to plug the phone in everytime you reboot the device to rejailbreak it vs a untethered jailbreak which doesn't really on a pc to perform the rejailbreak process.
The main changes you might notice from the update is better battery life, faster processing and so on.