DooMLoRD from xda-developers has been hard at work again and has just released version 11 of his Easy Rooting Toolkit. This allows users on the latest Jelly Bean firmware to root their handsets. However only select models are supported right now including the Xperia Z, Xperia SP and Xperia S.
The exploit used works on handsets with both locked and unlocked handsets, however it is also specific to particular customisations on each model. FTF firmware links are provided in each of the posts linked below, these can be flashed via Flashtool. For users that have a different customisation, they only need to flash the kernel.sin & system.sin and then run the rooting script.
Easy Rooting toolkit supports the following customisations:
Thanks DooMLoRD, skyend and @__poochi!