Jon,
I am not sure how necessary it is. But if you intend to do e-commerce (shirts, stickers, swag etc) it might be important to you. And who knows? If your puppet goes big then holding the trademark could be very beneficial financially.
I found this for TEAS filing fees :
http://inventors.about.com/od/inventing101trademarks/f/Fees.htmAnd this about how to copyright something:
http://wiki.answers.com/Q/How_do_you_copyright_somethingFrom that ^ it appears you are right about a creation being automatically copyrighted as yours. However, if you ever have need to defend the copyright it must be officially registered among other things like proving the infringing party had access (which may or may not be worth it). It also appears that copyrighting is less expensive for the protection. Trademarking is more about profiting from the images/personality.
Copyright isn't important to me personally as I don't have the talents to create the puppets and register all vids with Creative Commons license anyway, but should the day come that I want to sell swag or for some reason the puppet+personality is desired by a substantial entity, having the trademark to sell or transfer could ensure a kind of ownership.
I've thought in the past that it was either paranoia or dreaming too big to consider doing either given the costs; however, more times than I can count I have been asked if I have the trademark for the one puppet I do use. And he's not even on the radar in the big picture given his page hits and view counts. I figure when the time I invest mounts and if his exposure continues to grow, I'll do it. *eyeballing tax refunds*
