Our friends at Down By the Hipster pointed us to Muxtape, an "online mix tape website that recently launched and has quickly become the Tumblr for music. Now all you hipsters and wanna be DJ's can create an account, upload your songs, and send it along to your friends."

A quick look at the service makes it clear that some users are not uploading THEIR songs, but rather those of other artists. Is this authorized, and if not, of what consequence?

It's worth looking at Muxtape's limited terms of use, which simply state:

Muxtape is a service for creating mixtapes. Users may not upload songs from the same album or artist, or songs they do not have permission to let Muxtape use. Individual users may not create multiple muxtapes. Accounts not meeting these restrictions are subject to termination without notice. Muxtape will never reveal your email address to a third party. Muxtape is alive.

Certainly the the DMCA is relevant. Here is some analysis of whether Muxtape "on solid legal ground".