The oil example is a bad one. Yes you save a few bucks by doing the oil change yourself, but thats only true if you find the sale for $.99/quart oil. Otherwise the $14.99 oil change at a dealer is cheaper.

Then you have the time commitment, it takes you the time to drive to the store, shop and drive back and the time to do the oil change. Overall you'll probably spend an extra hour overall. Which is better spent working.

And don't forget, if you plan to be proper, you'll need to drive that old oil back to the store instead of dumping it down the storm drain.

So basically changing the oil yourself is not worth it. The only thing it gains you, is the ability to thump your chest and look down at all the "pussies" who can't change their own oil.