I use Mobil 1 and intend to just change the filter when it tells me to change the oil, and add a quart. I'm going to milk it for a yearly oil change or 15000 miles.
Synthetic doesn't break down as fast as petroleum based oils, so as long as it's clean, you should be able to easily get 15000 miles -- remember, I'll be adding a fresh quart & high quality filter every 5000 miles!