When you make a nearly perfect car, you take a big risk with any revisions.
That's the position Audi was in when it updated the A4 this year.
By and large, they did okay.
Styling changes are so subtle that you almost have to park an '09 and a '10 next to each other to see them.
One place where I think they missed it was the new taillamp design. I can't put my finger on it, but it reminds me of a car from years back...and it's not a good memory.