I use full synthetic on my 89 4runner. It has 150,000+ miles of pure abuse. I use the synthetic to max out it's life expectancy as much as possible. Since I know one of these days the engine will quit on me (it has detonation under load).

I will swich my 05 Burb and the 06 HHR to synthetic when they both have over 10,000 miles. It's hard not to when Wal-Mart sells the 5quart jug a tad bit over $20.

Ng