IMHE, all AIR apps "leak" over time (meaning, absorb more and more RSS as time goes on). This is regardless of whether they were written with Flash/Flex or HTML/JavaScript or a combination. I wrote a really small AIR app (one pane with some JavaScript, no images or other media) and it starts off at 100MB on boot and continues on until I kill it at well over 350MB RSS a day or two later. TweetDeck, Twhirl, FriendDeck, etc, they all leak for me, too, on both Mac and Linux.