> P1 recovered amazingly well after trying to save "Letter to Mr Smith 08/04/11", and getting the vile response "Error stating file '/home/ubuntu/Documents/Letter to Mr Smith 08/04': No such file or directory"
That's something I'd never consider, what with various directory separators baked into my subconscious.
This is the difference between products which have undergone long rounds of user testing and ones that haven't. For me this is one of the biggest issues facing Linux based operating systems today, because this is generally not an itch that people working on the project feel like scratching (see: design, documentation, etc.) With commercially backed projects like Ubuntu, it can get there over time, but I would look at a user testing result summary like this and say "we have a LONG way to go" if it was a product that I was leading.
That still leaves me a little ashamed on behalf of the industry. Why should any characters be disallowed?
Just for fun I tried saving a document in Microsoft Office 2007 here with a filename containing slashes. I got a slightly better response: "Ogiltigt filnamn" (Illegal filename). Not as confusing, but still no help at all on what was wrong with it or how to correct it.
I think it's tough to do, but certainly doable. What was outlined in the OP is just basic confusion amongst novices. Something that can easily be improved upon without hurting the experience for 'senior' users. I imagine this is how Mac does it. They throw their software up against the shores of a million and one newbies and iterate until they have a product that they are happy with. Testing is an integral component of UI design & creation, and from the looks of it, Ubuntu is slacking.