How often do drives need to be spun up?

Just from my experience in itself, I did not use an older HD (Nearly 10 years old now) for about 9 months, and once i pulled it out, it spun up like nothing had happened.

If you really felt concerned by it, you could plug it into a PSU and just power it on once a week or something.

I think this one may come from anecdotes about techs resurrecting dead drives by giving them a solid whack against a desk as a last resort (shortly followed by the story of a drive revived by a couple hours in the freezer). I haven't heard one of these war stories about a drive since the 90s - which makes me think the 'stuck' problem was unique to the construction of those old drives. Or the myth died out, is another possibility, I suppose.

I recently started booting an old PIII-800 computer which I first bought in 2000. It has two Maxtor DiamondMax D740X 80GB HDDs, which had not been used since 2006, and they work perfectly.

Car engines can seize when they are not turned over for a long time, with the oil draining to the sump and the bearings and pistons rusting, but the same does not apply to electric motors. It sounds like an urban myth to me.