The ww site actually has a little graphic on one of the pages about the flex plan that shows a small BUTTERED popcorn being about 12 pts. (That was based on a 7 cup bag.) I think in this case, I would guess on the high side.

I don't know if I can post a link here, but to see it, login to their site, click The Plan at the top of the page and then Understanding Points Values in the middle of the page.
Movie popcorn is in my top two guilty pleasures.
