Nautilus (GNOME Files) used to have a spatial mode, I was rather perturbed when they didn't bring it forward for GNOME 3. Obviously Apple killed the spatial finder with OS X, though it's always had the quasi-spatial mode with the pill button (remember that? I'm a little miffed about that one too, especially now that they've gotten rid of the dedicated full screen button that gave it the boot to make me hold Option every time I want to zoom a window instead of full screening it).
Fun fact: Nautilus was written by a company founded by Andy Hertzfeld and many of the initial employees were also alums from Apple's original Macintosh team.
Unfortunately the browser view has a habit of coming back - when you connect to a new network drive, or insert a USB stick, or just randomly. If there were a defaults bool I could set to turn it off forever, that'd be wonderful.
It makes sense to me that the sidebar is incompatible with spatial browsing. It changes the size/shape of the window, and the items there are a list of aliases that don't exist in that space.
