i always keep the lid on my pot, it's a large stock pot and the lid is not real heavy, and can rattle a bit to let some steam escape if needs be... but nothing comes close to keeping an eye on, and being withing diving distance of the dial on the stove...
the best times for a boil over are when you first add the extract if you are using extract, and it begins to boil, then the first addition of hops, then the second if you are boiling hops on a schedule. this has been my experience anyway.
i think throwing new things into the pot always stirs up the chemical reactions and gives you the potential for the boil over...
once the stuff settles down after you added (about five minutes and a few good stirs) it i put the lid back on... to keep the evaporation loss minimal, and to keep my overall boil consistent... my new stove doesn't seem to have the sack that the old one did when it comes to btu's...
anyone ever added more boiling water to the boiling wort as you lose volume, or would that be less desireable than just assuming your gonna lose x amount during the boil and start out with more wort?