fuel gauge accuracy

Hi all, to start I am a GM mechanic. My girlfriend has a 2003 Mazda 6 3.0L Duratec with the sport package (5speed auto etc.) I haven't dug into the issue yet but her fuel gauge is not accurate; will still show 1/4 tank of fuel left(or lately a little more) and the tank will be empty. Before I dig into electrical diagnosis, I was just curious if this is a common issue with these vehicles and if there are any trouble spots that I could be directed to first. I see there isn't much traffic in this forum but i've had luck with other vehicles of mine(mostly chevy/gmc) so I thought I'd give it a try.
Thanks
~Brandon~