I have a 2006 IS 350(bought in July with Sport/Nav/ML/Spoiler) that I drive to work(35 miles each way, 70 miles total a day). Let's just say I LOVE getting in that car and going to work. It's smooth, comfy, and I love the power. I'm an offensive driver and the car flat out moves. No more cars cutting in front of me at the last moment like when I had the car before this one( '97 Saturn with 124hp). I know you won't be disappointed with the IS350.
I have two kids (9 and 10 yrs old) that fit fine in the back. I've had 3 co-workers in the car when going to lunch. One guy in back(behind passenger) was 6'4" and said he was fine. The front passenger was a girl that was about 5'7", the girl behind me was 5'4". They all said it was not cramped, but wouldn't want to take a long trip with it(unless you had regular stops). The 6'4" guy couldn't sit behind me, as I'm 6'1" and have the set pushed back(not all the way back though).
Anyway, long story short. I love driving my IS350 over 70 miles each day.