Fast user switching and USB Kernel Panic
 

2 Questions:
Is there an equivalent to MacOSX / Windows fast user switching (and how to use it?)?
I have a nForce motherboard, a stock MDK 9.1 and when I plug in a USB device (may it be printer, scanner, mass storage dont matter), I get a kernel panic. What now?

no idea about the kernel panic

about switching users. You can login a second user by going to a text console - press ctrl-alt-F1 thru F6 for this - and then start a second X session by
startx -- :1
you can start a third by startx -- :2, etc. Then you can switch between the users by pressing ctrl-alt-F7 to get to the first, ctrl-alt-F8 to the second (F9 for the third etc.) It's faster than windows 'fast' user switching. This is resource intensive, though.

If you just need to be a different user for a few things you can use the command
su username
in a terminal window. Within that session you'll be the user with username.

Using gdm as login manager, you can start new session using the flexiserver. Mdk has it in its menus although GDM is not the default login manager.

Anybody know how that's possible in kde ?

The reason why it would be nice in a graphical fashion is that my other users are not happy with guessing under which Ctrl Alt Fx there session is.