Spool is a free iPhone and iPad app that allows you to save your flash video web urls and watch them later on your Apple devices. The universal app is free but the service is still under beta invite only. I happen to come across this free beta sign up under AppSumo. I tried saving the web links on my PC and it does save the videos on my iPhone.
Downloading of videos depends on your Internet speed. So if your Internet access speed is slow, it will be slow. You can give the service a try and let me know how you feel and drop me a comment in this post.