[RahCom]

There is definitely a cost-benefit analysis to run. How much is my time worth to me, how much gas do I use up in a month, what is the price of gas, and how much we this service cost?

I think that there certainly is a market for this sort of service, however I'd need to know a little bit more about the specifics to give a better answer.

[UnoriginalGuy]

All of that PLUS if you fill up my car too often then it is going to consume more gas (since you're using up gas by carting around a full tank all of the time).

[drharris]

That extra cost can be considered negligible. http://www.newton.dep.anl.gov/askasci/eng99/eng99630.htm

[im3w1l]

If you remove the cost of going to a station, so that a fill up is basically free, you could get away with driving on a quarter tank all the time. Assuming the service would allow it of course.