The iPhone 5 was successfully jailbroken on the very day of its release. Respected iPhone developer chpwn tweeted a picture of his iPhone 5's homescreen which included the Cydia icon on it in full 1136 x 640 resolution. He confirmed that it is jailbroken in a reply on Twitter to another iPhone developer i0n1c.
Grant Paul aka chpwn tweeted that the taller screen of the iPhone 5 likes Cydia too and he enclosed a link to a picture of his homescreen. Stefan Esser aka i0n1c then asked him if he had just compiled Cydia on a Dev Phone to which he replied no jailbroken. I'm sure there are plenty of people who would suggest that the screenshop was created using Photoshop or that it was a bookmark decorated to look like the real deal but the jailbreak community has developed great respect for chpwn over the past couple of years and he defintely has the skills to pull something like this off.
It may not be ready for the primetime yet though, but this is definitely the start and we can expect to hear progress updates over the coming weeks as the jailbreak community and the development teams get to work on creating a jailbreak tool for the new iPhone 5. Last year you may remember that it took a couple of months for the untethered jailbreak to arrive and since we are now dealing with a device that is packing a brand new A6 processor it might take even longer this time around. This really is a great first step though and we will be following all the progress.
For those who aren't aware, there is already a tethered jailbreak available using Redsn0w for A4 based devices like the iPhone 4 and 3GS running the latest iOS 6. We will keep everyone updated on the progress of a jailbreaking tool for the iPhone 5.