Ever here of the Exxon Valdez? Mobil is Exxon and vice versa. Granted any oil company is going to be somewhat enviromentally evil it goes with the business but Exxon/Mobil is blatantly irresponsible both enviromentally, politically and businesswise. They are very active in price fixing and price speculation, they give money only where their interests lie (have never to my knowledge worked to set up alt fuel filling stations i.e. natural gas at their current stations), they shirk clean up responsibilites when they do have accidents- taxpayers paid for 3/4th of the Valdez cleanup b/c it was cheaper to line the pockets of the Republican party (ruling party at the time).
Plus, in my opinion, their gas isn't real good for Subies. On the 5 that I've owned, Hess or Sunoco give me the best in both perfomance and mileage. Heck, I get better mileage with Sheetz gas then I do Exxon.