Does anybody know how it works with video sites that only have a web interface & flash player? I'm thinking of Tai Seng (http://mytv.taiseng.com/, a Cantonese movie site my wife watches that's based on the same tech as Crunchroll).
That said, Boxee has small handful of shows/networks that automatically switch to fullscreen for you – but those seem few and far between.
They do try to do two clever things with the box to make this better: Hit menu and sometimes there is a full screen button, sometimes not. Also, they try to place the mouse cursor over the "Fullscreen Button" in the Flash player, but this is wonky at best.