It's also worth noting that if you're having boilover problems you can turn the heat off and let the wort sit for approx 10 minutes right as it starts brushing 212F. That gives the hot break more time to coagulate and sink, keeping it from causing boilover foam. I used to do that when I had a 7 gal boil in my 8 gal pot, never a real boilover problem as long as I was paying attention. As soon as the temp hits 211 or so, I'd turn the heat off, have a beer, and turn it back on again. I have since started using Fermcap to help cut down on the ridiculous foaming I get during aeration and reduce blow-off as well.
On the other hand, it is definitely possible to boil over your wort from just excessive heat; the hot break foaming only makes the situation worse. Also, if your wort is really thick and syrupy (well above 1.100, say you're doing a partial boil but added all your LME/DME to 2.5 gallons) you can have boilover problems that fermcap won't help either. Fermcap just helps prevent boilovers and blowoffs by significantly reducing the foam-forming potential in the wort. Happily, it also drops out by the end of fermentation (I hear it adsorbs to the yeast when they drop) or else there'd be a problem with head retention.