The latest build of iOS has already been jailbroken! Thanks to the work of DjayB6 on the 4.3.1 jailbreak bundle and Universal Ramdisk Fixer, Apple's newest version of iOS has already got the jailbreak treatment.
PwnageTool 4.2 can be used to perform a tethered jailbreak for 4.3.1. This jailbreak method is not for the faint of heart, and is by no means considered a "stable" release for jailbreakers.
You will need several tools to perform a successful jailbreak of 4.3.1, and we have yet to hear about a stable untethered solution...