I have the MkII Sport, and find that it has great leg room and an airy feel to the interior (mine's black leather, black wood trim). I can comfortably fit 3 adults in the back if on a night out. I can also fit two kiddy seats with space in the middle to ensure the oldest won't bash the beejeebers out of the youngest when they arrive!
On a recent long weekend away to Cornwall I fitted in the boot:
-- Travel cot
-- 2 suitcases
-- Bag full of toys
-- My full car cleaning kit (always stays in the car)
-- Coats
It all fitted snugly, whereas in the IS I would have had to have piled up the back seat as well.
I've had the car since April, it's got 70k on the clock, and have needed one new wheel bearing (suspect the other one needs replacing too) which cost £150 odd to do (not thru' Lexus though) and in the New Year plan to replace the discs and brake pads as I'm paranoid they need doing, although I've been told they're fine for now.
Touch wood that nothing else has needed doing. The Sport has slightly harder suspension than the SE model, but I like the feel of the drive and am used to harder suspension through having the IS Sport and previously a Honda Prelude VTech.
My GS is T reg and cost about £12k with 63k miles on the clock and a FLSH and I bought it privately.
I definitely find it a good compromise between sporty looks and style and practicality. My in-laws have a Honda CRV (I also like Hondas) and they can't fit as much in their boot as I can in my GS!