I drove the 2008 535 sport & 550 sport back to back hard. My advice to anyone looking at both of these cars is this. If you can't feel much of a difference between the two cars, get the 535. I felt the difference immediately that is why I went with the 550. It feels very close in over-all performance to the 2001 M5 that I used to have. My wife had a different point of view but I used the Jedi mind trick on her value focused mind. She was happy enough with the 535 sport. I would agree that the 535 sport is 95% as good as the 550 sport for about 10% less money. I just happen to be one of those people who enjoy driving in that extra 5% zone and don't mind paying a little more for it.
Real time traffic with the nav. The car just looks mean.
BMW should get together with Apple to come up with a friendlier iDrive interface.