(Typing this on the FastSMSEvo keyboard in portrait mode - N900 sure has come far with so little manufacturer support.) Anyway, I'm pretty certain it unmounts it. Simply making the card/MyDocs unaccessible would be useless for the only reason that's even implemented - making sure the file systems/partitions don't get raped. Nokia execs might be stupid but their programmers aren't, mostly.

And, yes, were talking about corruption digitally, not physical damage.

So yes, that is different than making the cards inaccessible. (If cards were inaccessible but mounted, I'm pretty sure it would mess up your storage just about every time you used Mass Storage mode, without jumping through way too many hoops. Just a guess though, I am by no means an expert.)