one of my co-workers was leasing a new 6-series for a while and had nothing but problems with it.  bmw finally agreed to actually take it back and refund his entire lease.  one of my bosses has a new 5, and has had nothing but problems as well.  majority of their issues have been electrical.  and, unfortunately their bad experiences have made them never want to own a bmw ever again.
so, it's no joke that the 3 series is still bmw's flagship car for fun & reliability.  
i've had my 99 323i since 98, and honestly it's been the most reliable car i've ever owned- even more than my old honda civic.  the 5's, 6's, and 7's may look nice on the outside, but beauty is only skin deep.