I found vocaroo for what started out as a singing/impersonation contest on a blog that continued onto an email. (funny stuff). voice posts are getting to be common on blogs that I visit anyway.
This is the only place I've actually used it on anything other than music so far. I think I might have to try it on another internet community I'm familiar with to see how it affects the way everyone gets along, how it changes your impression of who you thought you were familiar with. too bad I didn't have this at aljazeera.com 5 years ago.

http://voicethread.com/#home

http://www.talkr.com/faq/what_is_talkr.html

http://www.vox.com/