Mobil 1 did have problems that caused gaskets and seals to shrink, especially if conventional oil had been in use for a long time. That problem was deminished when they upgraded to "try-synthetic" and became even less prone to the problem with the latest change.
The claim of the synthetic blends (not full synthetic) is that they give you most of the advantages of synthetic without the concern of increased oil consumption or leaks. These blends were made with high milage engines in mind, or so they claim.
My personal opinion is that synthetic truly is superior, but is also overkill. The performance of today's dino oil is very closely aproaching the performance level of synthetic oil.
I use Mobil 5W30 dino oil and I change it every 3,000 miles. As much as I drive, that turns out to be about every 5 weeks.
My $.02
