I just talked with them about flashing the VQ35HR ECM. I am fortunately located within a couple of miles from their office during the day, so I would drop off the car while they reflash.
Be sure to talk with them about your mods before sending in your ECM or doing it in person.
They told me that it costs $550 for the '07+ 350z.
There is some good information on their website:
http://www.technosquareinc.com