Driving habits and once the engine is started driving it at least 10 miles to evaporate water etc. is essential.
I go anywahere from 5000 to 12,000 miles between changes but it depends on the car and conditions. Not al cars can go extended drains even with synthetic.
By the way, there are rumors out there that the new Mobil 1 formula has fewer ani wear additives and is not as good as the older version. they are looking towards the new requirements post SL oils and more concern fo emissions, mpg and cat dmage then long term wear.
This is a great oil site by the way.
Pretty much unbiased from what I can see
http://theoildrop.server101.com/index.htm
