I've been lucky enough to have an RS4 for 3 hours today. So, here's my brain dump summary!
The car was white with black pack. White really doesn't show the lines very well in my opinion. It had 20" rotors which I though looked great in titanium and suited the car. I thought the car was a slightly strange spec in that it had dynamic ride control, dynamic steering and 20" Rotors but not the full Sports package (i.e. no sports exhaust). I'm up by Aberdeen and the temperature was -4'C on the way up to collect the car and once out in the Audi there was ice/snow on the verges so the roads damp and very cold. With that in mind though, the RS was absolutely planted, I was being pretty enthusiastic with it but it just felt stuck to the road. On comfort mode, it rides really well with the 20's. Change to Dynamic it initially felt a wee bit too firm however after getting out on to a quiet road and start to push on a bit it made more sense. One for when you're out in the mood yourself as opposed to with any passengers!
It felt pretty good in either auto or manual modes, in dynamic the downshifts in manual were particularly fun with the blips in revs, I'm looking forward to hearing if the sports exhaust is any better! I also found that in manual 6th or 7th is great for cruising but if you want to overtake you need to come down a couple of cogs as there isn't much pull. That being said, in the right gear it pulls like a train.
On the interior, I was a wee bit disappointed with some of the dash plastics when comparing to our current X5. Although the Audi looks more modern, the plastics around the dash don't have the weight or feel of the BMW. Even the manual gear shift paddles feel a cheaply plastic. The car had the standard Supersport seats which is what I've ordered. I had been thinking I should have spec'd the buckets but having tried the standard seats I'm happy with my choice. I did find the brake pedal to feel a bit high/close to the drive in relation to the steering wheels but it might just be having jumped out of our X5 it felt a bit strange.
I wasn't as lucky with the fuel economy as mentioned in some other posts, my average MPG ended up just over 20 but that was with a reasonable mix of town/dual carriageway etc. I should say though that I reset the trip computer after i had a blast which was showing 15mpg, but that was taps open in manual mode for about 10 miles

On the whole, I was pretty impressed. I'm lucky enough to have had a few nice cars over the last 20 years so my summary would be the RS4 is a mix of a few of my previous favourute cars - Porsche 997 for performance, current X5 for practicality and the Impreza/Evo of the late 90's for all weather ability.
Hopefully my Sepang Blue car will be with me for 1st March


RS4 by christopherjgrant, on Flickr