The Most Effective — TV ads or viral video?
Coast Capital Savings has recently made some appearances on YouTube! And it begs the question, which type of marketing is more effective: a full blown TV ad campaign or "leaking" some ads that they wanted to use but got vetoed?

If I were them, I would be simply leveraging YouTube’s unlimited bandwidth, easy interface, and great compatibility. That would allow me to embed videos onto my web site very easily.
I’d use it even if I didn’t care whether people were watching the video outside of my site or not, but I’m not sure what they are doing it for.
Oh, and about your question: I think it depends on your audience, I do not think the majority of our members watch YouTube, do you?
For our CU, the majority of our members probably don’t even know what YouTube is! It would enable us to reach members, and potential members, through another, possibly more attractive means.