I've always followed the "shut it off it you're sitting for more than 30 seconds" mantra,

I'm on your side with this one, loren.

When your engine is idling, it is burning gasoline. When it is off, it is not.

With modern fuel management systems, it takes no more fuel to start an engine than it does for the engine to idle -- there is no fuel enrichment with a hot engine; one second the engine is off; the next second it is idling at 800-1000 rpm and nothing unusual is going on regarding fuel consumption during the startup cycle.

As for wearing things out... the only thing getting extra wear is your electric starter. Well, maybe the alternator and battery have to do a bit of extra work, but nothing significant. I think I'd rather wear out my $150 starter than my $4500 engine.

This idling argument is related to the (mostly mis-informed) opinions of people who think they are doing their engine a favor when they start it up in the morning and let it warm up for 20 minutes before they drive away. Better to just get in and go -- assuming moderate use of throttle for at least the first couple of minutes. The engine will warm up much faster that way, and what wears engines out is how many times do the pistons go up and down when the engine is cold and the tolerances and clearances are not optimal. Sooner you get it warmed up, the better -- not to mention the extra wear on the engine just from sitting there idling.

Well, now I've probably gone and started a religious argument... so bring on the heretics and the true believers and get those torches lit.

tanstaafl.