All in all I got the K2 Pulse, their entry level boot and it has a pretty good lacing system too, no complaints, but yeah I'm sold on BOA, if it was utter crap it wouldn't be so widespread (don't quote me on that statement :X)
Almost any shop that sells Boa has a Boa replacement kit. I used to fix knobs and cables daily last winter, usually just minor shit that goes wrong with older boots. I've ridden Boa now since 03 and I won't go back, in that time only had a knob break cause I bounced off a rock and tree, and 2 cables had minor fraying so I replaced them.
Check your knob every once in a while to make sure it's tight, just like checking your binding screws.