quick comment, but "near 50/50" is as accurate as anyone (BMW, Mazda, Honda, chevy, pontiac, anyone) can get.
Most roadsters are around 51-53% front at curb, but passengers can shift the distribution on a typical roadster by 1-2% (YES, it's THAT much). The key here is seating position. Typical sedan passenger adjustments may only shift by a quarter or half percent. In other words, the passenger weight distribution can vary from 60% front for a 5 seat sedan to as low as 29% for a rearward seating position (think Lotus 7).
And the +/- 8 gallons of fuel have a direct effect generally on the rear weight and almost nil on the front weight (0% front, +/- 5%).
There's nothing magic about 50% either. Generally, anything lower than about 54% front at normal running condition (for some that may be 1- 145# driver, or for others it may be one 235# driver and 112# worth of safety equipment, or a 200# driver and a 115# passenger) has a very good chance of great handling qualities, depending on tuning and tire choices.
HAGD