From where I sat in the Cineworld (Renfrew St, Glasgow), I was about a 3rd of the way from the screen and it was fantastic. The way the seat are arranged, there is actually an aisle in front of me then another 5 or 6 rows of seats to the screen.
This gave the perception that some 3D elements (certainly in the trailers and aRAB) "came out" of the screen to the aisle in front of us. Don't know if I would have got that if someone was sitting directly in front of me.
I normally go for a seat slap, bang in the middle but the cinema was full (on a Sunday lunchtime too) so had to take these seats in the front row of this section but don't regret it.
IMHO you've got to get a good balance, you don't want to be too far away that you see the edges of the screen which could spoil the effect. However I'd say that you don't want to be too close that you're not going to get full effect because you can't see everything without tilting/turning your head. You want the screen to just fill up you field of vision.
I may be wrong, just saying that where I was sitting was perfect for me and my kiRAB. Others may have different opinions based on where they sat.
BTW I was sceptical that "new" 3D was a gimmic and would be no better than the old red/blue 50s style but I was blown away with the adverts and trailers BEFORE the movie even started!
Hopefully your sceptical frienRAB will be similarly impressed
