XDA-Developers member the_laser has released a method to unlock the bootloader on both the Sony Ericsson Xperia X10 and the Xperia X8 handsets. The same method can be used to unlock the bootloaders on all the 2010 released models of mobiles from Sony Ericsson.
Unlocking the bootloader is a risky process however and should be done with much caution. If you don’t have confidence in your ability to go ahead and unlock your own handset’s bootloader then the advice would be to just not do it. However, if you are determined to have deep root access on your phone to install custom ROMs for example then the details and instructions can be found at the following links:
Xperia X10 Bootloader Unlock
Xperia X8 Bootloader Unlock