I've had it a week & love it so far. I got an indicated 42.5 mpg on my way to work one morning, but I'm not even through my 1st tank of gas..er..diesel, so I don't know what my starting average is. I doubt I'll be doing much in the way of aero mods, since the car has a fairly full underbody cover already. I might be able to cover the center tunnel if I can avoid rubbing on the exhaust & not reduce my clearance too much. Also the rear 1/3 or so might have room for improvement. I think a lot will just be improving my own habits.
I think today I'm going to wash it (since we had snow 2 days after I got it), then maybe I'll have some pics to post.