I honeslty don't know when exactly Linux added the feature to let you swap desktops easily.

That would be about 1965, or whenever it was that UNIX was conceived. UNIX has had the capacity to support thousands of users simultaneously since the beginning of time (literally). When X appeared in the late 80s, very little changed in this regard.

Since Windows 95, Microsoft has been trying very very hard to add sensible multi-user facilities to Windows. The fact that consumer releases prior to XP were unable to prevent users logging in without a password, let alone prevent users from having full write access to each others' files, is perhaps irrelevant considering those users each had permission to delete the Windows kernel as well.

The NT kernel supplied XP with the capacity to handle multiple users securely and XP introduced fast user switching, but the damage was done --- most of the apps available by that point had to be run as root, and the attempt to bring the system a tiny fraction further along its long journey to UNIX-level user security was one of the more significant nails in Vista's coffin.

I reckon MS will eventually (too late) do what Apple did (also too late) and replace the entire thing with a bastard UNIX system running the shell from the previous system, and provide a compatibility layer. Indeed, it might be the only way to save it. Meanwhile, Wine continues to make it increasingly obsolete.

for a Google router there's no particular business model other than spying on the owner

You are aware of the idea of selling routers, right?

I've seen this advertised on TV in the UK for a production car, I think it was the V70; and it's mentioned in the first sentence of the Safety section of the S80's website: http://www.volvocars.com/UK/ALL-CARS-MY09/VOLVO-S80/Pages/default.aspx... they call it Collision Warning with Auto Brake. Really, this is old --- the current model of the S80 is a couple of years old at least.