Proximity sensors are good for scaring the crap out of people, and knowing when chavs are
near your car rather than actually twitting it.
Bad for when it's raining, trees nearby, leaves falling down etc etc etc...

Deffinately get remote central locking, I could not be without it now, it's great for when it's pissing down and you want to get inside very quickly, or if you've got lots of shopping it's easier to press a button than muck about with keys.
I've got a clifford 600 (or 650 or something, I forget!) myself, it's pretty nifty.