http://watchlaterapp.com/ will do offline caching (including Flash videos) to your iPad, but it's only a web/iPad service, so I'm not sure it ticks the "multiple device" box.
interesting, though I just signed up and my video player was empty, and I'm hesitant to pay for their iPad app.
That's one of the things I like about the onboarding experience with Shelby.tv; when you sign up, you can start watching what your friends are tweeting/sharing since it pulls it from you twitter/facebook accounts.
