This post by Ivan (um_lunchbox) over at the Scikotics forum is very interesting. >
http://www.scikotics.com/forums/showthread.php?t=48640 Some of you may have already seen it, but just in case you're interested in achieving incredible gas mileage in your xD, check it out.
Last weekend I was able to get 45 MPG while drafting behind my buddies racecar trailer. I used the cruise control and hovered at 60 MPH for over one hundred miles. My tire air pressue is bumped up 4 PSI over reccomended pressure (still within the safe zone). Even without that draft I can usually get between 37 & 41 MPG using these techniques. If mileage is of no concern, then this stuff wont matter. But the results are impressive and worth checking out if you are trying to save money etc.
I guess hypermiling is nothing new, but it was an eye opener for me, hope it helps.