I remember reading somewhere that you should never cover the pot when boiling wort.
Is this true? Does anyone know why this is?
DO NOT COVER. Take a gander at this: Dimethyl sulfides - Home Brewing Wiki
I believe you are supposed to leave it uncovered so that the DMS (or something like that) will boil off and not cause any off flavors. I don't think it is as big of a deal when you are using extract, but it is still a good idea to leave the lid off.
You can cover while the wort is coming to a boil. Some cover partially while boiling.
Covering while boiling causes compunds that form DMS, Di-Methyl Sulfide togo back into the wort thus causing off-flavors.
Interesting.. Thanks guys.