I simply love the S4 - especially with the manual trans and in wagon format. It is the perfect daily driver for me, and a really nice compliment to the X5. The S4 is a bit on the rough side for ride - certainly compared to an X5. But it rides nicer than the E46 M3, it's closest competitor. I much prefer a V8 over the high revving I6 - which is a gem of a motor in it's own right, but not as good for normal street driving. The recaro seats are simply superb, and the interior is as good as my benchmark in that category - E39 M5 (which I have owned). I highly recommend them - especially if you live where it snows. I am an avid skiier, and with dedicated performance snow tires and Quattro, it is simply unstoppable. The only limitation is ground clearance, but as long as you drive on reasonably maintained roads there is nothing the car cannot do in the slippery stuff. Driving it in the rain is the same as the dry - grip is fantastic. And I am getting great wear out of the tires, which are not at all expensive to replace - 235-40-18's, and plenty of choices - I run summer tires, which do great in dry and rain with the Quattro. Anyway - I can't say enough about the car - best daily driver I have ever owned by a big margin.

Do not be afraid of maint - mine has been bulletproof so far. 76K miles and counting. The engine is a bit tight and harder to work on than some - for example you have to pull the entire front bumper assembly just to change the drive belts. That is a PITA. The valve cover seals go at ~60K miles or so and are not the easiest things to change. Spark plugs, fuel filter, air filter, oil changes - normal maint is very straightforward. Needs plugs every 60K miles. Generally maint is pretty similar to a BMW - nothing out of the ordinary and very much on par with any German car. In fact, probably less costly than a BMW or MBZ - the parts are not too bad. Service costs seem to be similar for anything these days. I mostly do the work myself. I am still on the original clutch too.

There is really nothing to be afraid of on these cars, IMHO. Rather bulletproof. Very much like BMW's. I expect the motor is good past 200K miles with proper maint and 7500 mile oil changes. Factory service interval is 10K. Oh - it uses a rather large amount of oil - close to 9 qts. So oil changes are not cheap. But BMW's are in the same ball park there too.

My only caution - stay away from the 04 model. That was first year. They had some issues including some motor issues. You don't need that. everything seems to be corrected fully by 2005 model year. Mine was built October 2004, but is a 2005 MY. So stick with 2005+. Body style changed to B7 in 2005.5. Might be better off with one of those, but I prefer the lines on the older body myself. Mechanically they are nearly identical - the diff split changed from 50/50 to 40/60. So the B7 is slightly better in dry, B6 is slightly better in wet / snow - but pretty close either way. No other changes to speak of other than minor cosmetic things.

Get one - fantastic cars at a great price point right now.

Oh - and as to the trans fluid question - I decided to stick with BMW's recommendation and leave it be. Doesn't make sense to me to change fluid at 100K mi the first time. Maybe if it had been done at 50-60K. I will change the TC and diff fluids, however.