I found a post on another forum and found it interesting and also a little alarming. It seems that the Direct Injection can cause carbon deposits to build up over a semi short period of time on the intake valve. This can cause a loss of power. There are documented reports on the BMW, the Audi and the VW, so I would think that it happens on other DI engines. It appears that the assistant GM engineer for V6 engines is aware of the problem.
here is a link to the article,
http://www.edmunds.com/autoobserver-...-adopters.html
I would hope that with GM being aware of this potential problem, and with over 6,000 CPU hours spent on the LT1 combustion chamber design they have addressed thsis