I remember hearing a cheap form of copyright is to mail (not e-mail, snail mail) yourself your music and not open it, so if someone uses it you have proof that it's existed before they released it with an unopened envelope/box/etc. containing the music.

Would this be acceptable evidence in court, or are people talking out of there ass?
It isn't an official copyright until it is registered with the government. Other forms of copyright are just proving the work is yours, like mailing it to yourself and not opening the envelope so you have a date the creation became yours on the package.

Another easy way to do this is myfreecopyright.com. Or read the copyright thread, Chris knows his stuff.
The "poor man's copyright" holds very little actual weight in court. Time-stamped computer files have about as much credibility. Now, you COULD upload everything to a third-party website, which would have a little more credibility, since you have a third-party saying "Yes, this music has been here since ________." However, the only way to really protect yourself is to register with the copyright office.

Besides, if you want to claim infringement, you can't do it until you register regardless.
My guitar modification blog.
Quote by MuffinMan
Jesus was all like "To those about to rock, I salute you." then he grabbed his mighty axe and rocked the Romans out really hard. Of course they were strict classical music so....
This ^

Note it is part of the copyright for dummies sticky.

Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.