Change it at 5k miles. I was shocked to read the manual for my wife's VW Passat and after 10k miles the oil change interval is every 10k miles. Here is an interesting bit though...the service light in the dash comes on every 5k miles.
I actually find that my xB gets more efficient about half way through an oil change and that when I change the oil I get slightly worse fuel economy for about 2k miles. I am currently just over 4k miles from my last oil change (so less than 1k miles to my next oil change) and my last two tanks of gas have been over 30 mpg which is as good as I have ever seen.
