I use Mobil 1 also.
I have been told not to use it in an engine that has been used with conventional oil.... wrong..
I have been told it is worthless, and ruins engines because it is no better than conventional...just more expensive........ wrong
I have heard people who love it, and those who've never tried it, but are too cheap to pay the price, and therefore complain about it.
I have seen my cars engines seem to get better milage, and even a nicer feel, and smoother running since Mobil 1.
I drive around 25,000+ miles in a year, so, Mobil 1 makes sense for oil changes alone.
Here is alink to a site that did a nice test and review on Mobil 1 , and this was before Mobil rated it at 15,000 miles:: http://neptune.spacebears.com/cars/stories/mobil1.html
Keep in mind, you should change the oil filter every 3000-6000 miles, and always check and top off the Mobil 1 oil. These are important to long life.
One more thing that is suggested by some folks, and this might be different with specific engines. I was told to go one step higher in thickness for some engines, as Mobil 1 is slightly thinner than conventional, especially after it breaks down....and it is also recomended for high mile engines. I usually use what is called for. My Caprice, however, calls for 5w-30, but this time I used 10w-30, and the engine feels much better.