We have had a few debates about this at my (Gundy's) house which I shouldn't go into.  Let's just say it can really depend on the individual car.

As a shade-tree mechanic, might I remind you that running your car down to fumes regularly can cause expensive damage to your fuel injection system.  (But I know, you have to get there now!!!)  That said, it is good to run as much old fuel out of your vehicle as safely possible every once in awhile, so you aren't running on old gas.

Generally, it's wise to keep your fuel tank above half full to prevent lots of condensation buildup which can hurt your car's performance.

Thanks to 9 News Denver for this cool chart, which works wonderfully if you have one of the 50 most popular cars in the U.S. right now: