Flash's little brother Javascript is climbing up there as a Thing To Avoid too, but much more complex! The signature case is Chessbase, who last week decided to do live pulls from its game server, making me want to block scripts on the news summary page, and then turn it back on to use the game replayer script!
Since I'm no genius with NoScript, I just toggle that QuickJS addon back and forth all day!
Tumblr is up there with the world's most obnoxious slider! if your mouse strays over the "Facebook Icon", the ENTIRE page slides to the right to show a "Like us" ad! But if you totally turn Javascript off, then the auto-pic-loader stops working! At least Element Hiding Helper for AdBlock helps a little there!