YouTube Owns YourStuff (So does YouTubeTwo)
In its Terms & Conditions, the wildly popular video sharing site YouTube emphasizes that "you retain all of your ownership rights in your User Submissions".2) Don't post in the open:
There's quite a large "BUT...", however. Not only does YouTube retain the right to create derivative works (emphasis mine), but so do the users, and so too, does YouTube's successor company.
In case you haven't been following the news for the past few years, the RIAA will be more than happy to come after you for doing that. While the tv show and movie bigwigs haven't gone after vids much (arguments can be made for fair use re: clips vs. episodes/full-length films), the music industry is BAT-SHIT INSANE about musical artists' tracks being posted anywhere they can be listened to/downloaded for free (and yes, btw, you can download off YouTube if you know how). It doesn't matter how the song is posted; you've shared their material for free and they are completely mental about it. Ask the people who run the AMV, who had to take down hundreds (I believe) of vids after hearing from various recording artists' labels. Ask people who have been sued (not just issued C&D letters, but sued) and had to pay for downloading music.
3) How to host vids as safely as you can:
Set up a subdirectory at your own domain. If you don't own your own domain space, find someone who is willing to share. Password-protect the sub-directory using an .htaccess file. Don't use the name of the song in the filename of your vid (example: if you've vidded Buffy to Bring Me to Life, name the file BringBuf.zip). (Oh, yeah, zip your files to avoid hotlinking menaces.) Put spider-avoiding code in your .htaccess as well. If you don't know how to do these things, ask.
Bottom line - vidders create and host illegal downloads, plain and simple. Don't be stupid about it.