Theres a convertor called Orbit Downloader and it downloads most Flash and Videos, it's also its own Download Manager
this actually reminds me of a windows based tool (freeware), wherein you can download the videos from youtube in a .flv (to your pc) and then convert it to a .avi format! that's faster then most of the online video converting sites appreciate your concern though!!
I found the solution from this blog. Because there are so many way to download and stream online videos.
I wanna share my experience that i am on ubuntu and it automatically downloads the file when played in youtube i think that the best.