There are a few drawbacks that are annoyances for me. My specific phone has a locked bootloader that cannot be unlocked. As far as I can see, it seems to be quite arbitrary whether the phone you get has an unlockable bootloader or not.
Also, I already had to get my phone swapped due to the "yellow blotches" screen proble, which was a painful process, took far too long, and saw handled badly by Sony. Now, my replacement phone is getting a yellow tint. I really cannot face going through the Sony repair centre process again, so I'm left with a defective handset.
Also, the ICS update (which took too long to arrive) has left my phone somewhat laggy, so I'm having to either put up with this, or revert to GB. Neither of these options should be necessary on a well QAed phone.
Hopefully, I'm just unlucky. QA and customer service issues aside, it is a good phone, especially if you are not too concerned about being able to carry out functions that require an unlocked bootloader.