From a band's perspective, I find the 'like' to hear music thing really lame. Actually, I think the whole 'like' thing on facebook is crappy overall.
We currently have some music up for free download and we'll have a new EP up in a few weeks. I think we're going to allow free streaming of the EP and if someone really wants it, they can join our mailing list on our website and download the entire EP for free. I'd much rather have an email address than a 'like' on facebook.
Also, at shows we're going to have a tip jar.. Take a CD and if you are inclined to leave a few bucks, great.. If not? Great! By all means take our CD and spread the word..
For an unknown band I think exposure is far more important than a facebook like..