I have a 2008 4.8i with most options including sports package (20" wheels).
Overall: It has been a great experience so far. The handling is great -- a normal SUV cannot compare to this. I do have summer and winter 20" wheel & tire sets.
Repairs: Just checked my service records. Had very few problems over 5 years (but I have only done 34,000 miles). All covered by warranty, but (from worst) they been CID replacement (iDrive screen dark) ; condensor leak fixed (impacted A/C); rear view mirror replaced (due to compass not working); passenger side visor replaced; peeling headlight switch replaced; and finally one front daylight running light replaced. So actually VERY few problems...
Negatives: As mentioned already, it just eats through the 20" tires. I have continued to use the Run-Flat tires so my ride may be a bit harsher than some might like. Average mpg is only 14 but that's due to the way I drive