I use both the US keyboard layout and the Finnish one. My keyboard's physical layout is the US one, and it's rather more convenient for writing English and code. However, sometimes I need to write Finnish or Swedish, and so I use the GNOME keyboard layout switcher to switch between them.
If I forget to switch back from Finnish, I invariably have a few moments of panic, when I suspect I've had a stroke, or have inadvertently drunk a bottle of vodka, when my computer doesn't obey my keyboard.
Lars and friends