First and foremost, the XC60 exterior style has more of a cool factor while the X3 is a bit more reserved. I was impressed by the performance of the Haldex AWD (during the 20 minute test drive), and it seems the vehicle is very programmable and can be tailored to fit like a glove. Things that concern me slightly are the navi (cumbersome) and the interior finishes aren't particularly interesting. Fuel consumption isn't great either.
While the X3 style is more conservative, it's not a deal-breaker. The interior is very slick, the seats in the M Sport are amazing and the overall power is great.
I didn't experience the XDrive to any real degree and while I have zero plans to take this offroad, I want to know how it performs on dirt roads and in slippery weather. What about the audio? That's important to me. And iDrive? People seem 50/50 on that.
Anything else I should know or think about?