[puddleglum]

A good oil should grab the dirt and combustion by products and hold them in suspension. This will make the oil look dirty, even if it may have some useful life left.

I agree that short trips and cold engine operation are much harder on the oil and the engine than longer ones. Oil won't last near as long with lots of short trips. My first experience with syn. oil, I was advised that it should be good for 15,000km. Well, I took their advice, and didn't change my oil for the next 2.5 years(read young and foolish). It rarely ran more than ten minutes at a time, and by the time I changed the oil, my engine was so full of rust from condensation that it was almost ruined.
I now do my best to make sure the car gets warmed up as often as possible and it isn't driven on a daily basis. I'm thinking that a good synthetic oil could probably handle an annual OCI. I will probably stick with 6 months though until the warranty runs out.