Do you use Macromedia Flash in your websites? While it gets some bad press (SEO and usability-wise), it’s got a lot of good uses. YouTube, and other video-sharing sites, use Flash to play videos. Some sites have Flash-animated logos. A lot of online games are made with Flash.
A common annoyance with Flash “movies” (the term for Flash files) is that they have a static size. While you can scale them by hard-coding pixel values into the embed code, there’s no easy way to have a Flash movie automatically scale itself to fit its parent element.
FitFlash looks like a great library, though I (currently) don’t have much need for it. If you work with Flash a lot, look into FitFlash.