I'd agree that the tinting does reduce the temp inside the car. Having owned both tinted and non-tinted cars the one with the tinted windows was always a little cooler in the summer. However, backing up at night usually meant rolling down the windows to see the mirrors (but a good hypermiler shouldn't be backing up anyways
)
As for the tint jobs, I wouldn't do it myself just cause I see TONS of cars with hundreds of bubbles in their tint jobs...especially the back windows. I'd guess that if they had a shop do that it'd be covered under warranty so it probably is only DIY ones that end up that way...at least that's my guess.