A few months back my roommate's rare house plant was dying. In a last ditch effort to bring it back to life, he enlisted my help. We scoured various message boards and Q&A sites with little success to get help identifying the plant (he got it as a gift).
The plant ended up going to that big greenhouse in the sky. The experience made me realize there's a pretty basic need for sites, such as PicAnswers, which lets anyone upload a picture and ask a question about it. Interestingly, the amount of high profile Q&A services that don't let users do this is surprising. One of the few to allow it is the AOL-owned Yedda, while sites such as Yahoo Answers, Microsoft's QnA Live, and Amazon.com's Askville are limited to text.
Like Amazon's Mechanical Turk project, PicAnswers is driven by humans. People upload their photos, and other users chime in if they can answer the query. A lot of the questions posed on the site range from simple identification issues like "what the heck is this?" to advice about what to do about a problem posted in the picture.
Despite its simplicity, PicAnswers is missing two very helpful components: a way to vote on other user's answers to help filter down the best responses, and a karma system that makes it worthwhile to answer other people's questions. As it stands, you're left to sort through the answers yourself and answer out of the goodness of your heart. I'm hoping the site's creators add these soon. In the meantime, it's definitely worth bookmarking for the next time you unearth something that needs photo identification.