[johncoltrane]

Start GVim, it acts as a server named GVIM

    $ gvim filename

Open another file in the same GVim instance

    $ gvim --servername GVIM --remote otherfilename

[duaneb]

can you ctrl-w-w to focus between X11 windows?

[johncoltrane]

With this setup you have only one GVim instance that works as usual. Switching between this single GVim X11 window and other X11 windows from other programs is your WM's business, not Vim's.

[duaneb]

Ah, well, I can dream.