Technically, if it's not yours, (that is, you didn't create it) and you don't have license to reproduce it (that is, you didn't pay a royalty for its use) then publishing it is copyright infringement.

If someone produces a video using an unauthorized audio track, then publishes it, this would be copyright infringement. Now if you happen to link to their video, while not in direct violation yourself (so you're safe, one supposes) you are still giving a nod to that person's infringement.

Once something is posted to YouTube or any other media upload service, it falls under their Terms of Use, giving them complete freedom to remove any video they deem an infringement. They may even revoke a user's privileges, if they so wish. There is a clear declaration made by the user that they own and have the right to publish whatever they upload. Clearly, if it is not theirs, they are in violation of the TOU.

It is not a monetary question. Reproduction and redistribution, even if it is for free, is copyright infringement, plain and simple. Just copying a CD and giving it to your friend is infringement.

Link: Copyright

Link: MRI: Music Licensing, Royalty Accounting, License Administration

Link: Music Publishers' Association | Copyright Resource Center