I just got finished changing my oil in my MP3 literally 5 minutes ago. I've used Mobil1 5w30 since I got it, along with the Mobil1 oil filter (car has 37,000 miles on it). It costs a little more, but I've never had any problems. The best thing about synthetics is that you don't have to be as "on time" with your changes. I usually shoot for around 6,000 miles, but if it's cold or rainy you can put it off without worrying.
On the other hand, my '94 Ford Taurus has around 200,000 miles, and I use whatever oil is on sale with a cheapo filter. It's never gave me any major engine problems either. (dunno)