Went to the Metreon and had stale cold popcorn (which I still finished). They had huge yellow plastic bags full of popcorn that they pop during the deadtime and horde up. Usually, they'll serve you from the popper if it's going and you ask, but it was off when I got there.
This made me thing about which movie theaters have the best popcorn. I vote for the Red Vic by a comfortable margin, which only has one screen and pops fresh before every showing. The popcorn is served in large wooden bowls and there's always yeast. Always. Castro is OK, they don't pop as often as they should, but they usually have yeast. The Landmark theatres are also pretty good, especially the Bridge, where's there also only one screen (so frequent popping) and also has yeast. Last time I was at the Lumiere, they only had salt in glass shakers in the lobby, so I couldn't take packets with me into the theater to resalt the middle of the bag. The Embarcadero has a big rack of shakers with specialty topping powders, (some of them are really gross though, especially the sweet ones) and usually has yeast (although they were out the last time I was there). The Century theaters serve Kettle Corn, which might be delicious except they just put tubs of it in heaters and take them out as people order.
I actually don't like butter on my popcorn, so I can't speak to which place has good butter. I don't think anyone actually serves real melted butter anymore, and the oily stuff that is usually served doesn't sit so well with me.