When I open GIMP, I would like it to appear in maximized single-window mode. Is there a way I can do this, either with a shell script or preferences option?
If yours is Gimp>=2.8.2, which it most likely is in Ubuntu 12.10, You can simply select
and you will get gimp in single window mode the next time.
As for keeping it maximised, install maximus from Ubuntu Software Centre.
and all the windows you open will be maximised. You can set maximus as an autostart app (the command is simply
You might need to perform what inLoveWithPython said earlier, then go to Edit > Preferences > Window Management and uncheck the box that says "save window positions on exit" and click the button that says "save window positions now."