I agree that it's important to protect your identity. What could anyone gain from identifying an avatar pic though? Unless you use the same av on diffrent sites.
I don't know of any other reverse searches. I'm sure the mods must use Tineye to identify some users' stolen pics.
Think about it. You're missing the obvious.
It would matter if your avatar pic came from a photo that's on your FaceBook page, blog, online photo album, someone else's online photo album that identifies your name, etc. Many people like the same images so much that they re-use them in different places, unintentionally linking an anonymous identity with a public one. For instance, my company's website has a lot of personal information about me. If I unwisely chose an image that can also be found on my own company website, then people who have seen me on cam would recognize my photo there, know my name, and where I work if they used TinEye to find that website. The same thing could happen with FaceBook, MySpace, LinkedIn, blogs, etc.
I was just using my avatar image to demonstrate that TinEye "sees" avatar pics. I would not have posted that link if it linked to any identifying information about me. I'm obviously concerned about images that are not my avatar pic, or else I would not have used it as an example.