I always blame the users. Basically, just disconnect the drive (by ejecting it in some way shape or form) before running Software Update.

Your second paragraph is just fine, except the bit about the DIY gene--some people just go nuts. See url=http://www.xlr8yourmac.com for the crazies.

eSATA will be a problem, of course, unless you have a card for it.

There's also some issue with NCQ and the newer machines, so just avoid those drives--but if you're talking externals, you're fine.

I am the Doctor, and THIS... is my SPOON!