Feedback is a vital part of the logo design process, and the forums listed here can offer fresh perspectives on your design projects.
Since publishing this post a few of the resources have either disappeared or become virtual ghost-towns, so I removed them. An addition, though — Ivan Raszi pointed me toward his new critique section on Brands of the World.
Where do you learn online?
Have you had any personal experience with the forums above? If you know of any other forums or sources of online critiques, do let me know in the comments.