I turn 60 this year (which blows my mind) so my autocross cars were accordingly old: heavily modified '70 240Z and '70 Opel GT. Slow by today's standards, but back then they were a blast. Canyon roads with the wife on board. I might as well be driving a neighborhood ice cream truck.
As for my S5, I am extremely pleased with the reliability. I've got 86K on it now. Since I keep a car for at least 10 years and 200K miles, I change the oil every 5K. Oil useage is higher than other cars I have owned - it uses almost a quart between changes. I've just had to get used to that. There has been 2 factory elements that needed replacement. First, the sport diff seals had a tiny leak at only 1K miles. The warranty fix was quick and there has been no recurrence. The dealer mechanic said that there were a group of diffs with that problem. Second, I just had a fuel injector go bad at 85K - its replacement was covered under the extended warranty.
I've had the carbon cleaning done twice as a preventative measure.
As for the struck-by-lightning problems, I've had a couple. My radiator got whacked by a giant bolt on the freeway, so I had to get it replaced (I had my mechanic install a metal mesh behind the grill to prevent a recurrance). Also, there was a recall for a reflash on the ECU - when the dealer did the reflash, it killed the box so they had to replace it (at no charge to me). One thing that is irritating, but I just deal with it, is having more dropouts on Sirius than other cars. Researching onlne, that seems to be a common weakness for Audis.
It still looks great. The black paint is still flawless despite getting to live in the desert sun. The seat bolsters have none of the wrinkles and creases that form on other manufacturers sport leather seats. The interior looks new. There are no squeaks or rattles in the body or interior. Window and door seals are holding up well - there is no wind noise or water leaks.
I have the 6-speed manual. Because I do a lot of highway driving, I still have the original clutch (my A4 clutch lasted almost 100K miles). The trans synchros are holding up very well - it shifts like it did when new.
As for gas mileage, I average just over 19. On a weekend run to Palm Springs, I filled up just before getting on the highway, paced traffic (~75mph) ran the tank low and jumped off the freeway to fill up. I was really curious what a pure highway mileage number would be. I got 23.9mpg.
Hope this helps.