http://xbox360.ign.com/articles/910/910279p1.html
"Now, before you get excited about laying down the note chart for your favorite song that isn't in the game using the, there are a few things you should know. The first is that there is no vocal stream in the song creation tools. You can put down a keyboard part and have someone sing it, but dictating the words or recording your voice is out. The second is that there is a three minute or 1,200 note limit on user created songs. Since you can upload the songs you create in the studio and let others download them, keeping a limit on the size of the file is a necessity. The last, and perhaps the most important caveat, is that prior to uploading a song you'll have to agree to a user agreement which states that the song is your personal work and not copyrighted by someone else. Any copyright infringing songs uploaded by users will be promptly removed. But hey, you can still create them and just play them locally if you want."
I knew about the first one, but the last two are news to me.
