 I've owned my 2004 S4 for almost two years now (bought w/ 15k miles), sufficient time both to get over any new car puppy love and to notice any reliability issues.  Well, I'm still in love and the only reliability issue was a balky sunroof switch that was replaced under warranty.  At first glance, it appears to be a mild-mannered A4: solid German engineering in a conservatively styled sedan.  But once you've settled into a front seat that holds you tight and heard the V8 grumble to life, you know this is no A4.  A few corners at high speed and one highway on-ramp are all that's needed to confirm that you're driving an agile machine that carries speed deceptively well.