This thread looks a little old, but I wanted to share the contact info for the shop that did the tint on my 2008 335i. I got 20% all the way around, including the front and back windshields. 20% is probably a little dark for the front, but the car looked great, and a I haven't had any issues with the tint.
The 2008 is for sale, and I plan to have them do my 2014 once it arrives from SA.
Located in Lawrenceville