Already do that. Bonus: I'm on a laptop intermittently without internet access, and can open up PDFs to read offline without having them be lost when my browser crashes.
> Now if someone can provide a means of un-embedding streaming video as well, that would be very useful.
Really hard to do, unfortunately. For HTML5 video, maybe (and I'd love it if someone came up with something of the sort), but for flash video the problem is that there isn't really any standard for flash video players, so you can't really parse the flash file to figure out what video to play without running it.
That being said, maybe some sort of local proxy that recognizes when a video file is requested by flash and reports a 404 to it, with a popup "do you wish to open this link in a local player". But that way lies madness.