Yes, okay, technically it is "damn it", so obliterating the space between them implies a sense of urgency, potency, hurriedness. BUT, there's something lost in the spirit of writing out "damnit" as opposed to the colloquial "dammit".

The latter bespeaks a feeling of abandonment in the face of emotion; the former makes only a conciliatory nod to real passion, but within the confines of staid, dryasdust proper convention. Like they can never really let loose and swear but must do so only within acceptable guidelines of format. I know this is coming from someone who's usually a prick about grammatical adherence, but I value creative liberty to a point. This isn't intended to be a carte blanche for spelling errors and illiteracy. There's a difference between creative liberty, and pretending to this to cover up one's own inadequacies, like how the British like to pretend Americans don't understand "sarcasm", when actually they just said something fucking stupid.