Or, setUpInstance looks like it's the setter for an upInstance variable, whereas setupInstance has an obvious connection to the "setup" action even if it's grammatically incorrect.
Haha, very true. That is one reason I like underscores: you can distinguish between setup_instance, set_up_instance, and set_upinstance. Or maybe set_up_upinstance. In context, it probably wouldn't matter unless you have both "setup" and "upinstance" types running around.