700 Mile club Who\'s in?
Yosemity, driving slower is the #1 thing you can do to improve your mileage. Check your tire pressure -- put it up near the max rated for the tire, unless the ride is too harsh, or they start wearing unevenly. I have been running the OEM Goodyears at 40-44 PSI since day 1 and they are evenly work at 44k miles.
BigDaddy... you say the light came on at 700 miles and you got 50 MPG? If you were fully vented, 50 MPG should take you a bit beyond 700 miles... more like 725 or 730 (until the light comes on). Maybe you weren't "fully" vented? You may want to do a ventectomy. It takes 5 minutes and you can fill up easier without waiting. Also, you'll know it's really all the way full.
Also, your light could be calibrated wrong. It can be reset with Vag-Com (I assume that still works on a PD). You do have to drain the tank, though. At 50 MPG, you should have about 830 mile range... but I wouldn't try to take it too close to that... you don't want to run out!