The thing about reducing weight is you have to keep in mind what you are compromising. I'm planning to move up in wheel diameter, width, tire width and as a consequence rotational weight but I'm doing this for other reasons. My car is missing about 400-500lbs of dead weight, including cruise control which is one of those things that might help gas mileage....if it doesn't make me fall asleep and crash into a tree during a 50 mile plus drive.

The lower you go in weight the more it matters of course, going from 6000 to 5800 is laughable in a full sized truck but even 100lbs from an old VW (that weighs under 1800lbs) can be HUGE. F1 teams at some point complained to Champion I believe that the spark plug was THE densest part in their cars, as a result the spark plug design seen to the left was put into production, on the far right is a Ford Taurus plug for comparison's sake.

http://www.caranddriver.com/var/ezwe...line_image.jpg

You just have to ask yourself "how serious am I about this?".