Idea for Default Avatar
I love what you have been working on. I have a suggestion for the default avatars.
I love the professional look of the Mystery Man avatar, but the downside of using it is that everyone has the same exact default avatar.
It would be nice if you created a new set of default avatars similar to Mystery Man, except it changes the background color for different emails, and then uses a consistent color for that email address.
You could probably use some algorithm that spits out the same result for each email so that each email address is always the same color.
This would be useful in forums and blog comments where people don't always have a registered Gravatar or Libravatar. At least their replies would have the same color default avatar, so it is easier to tell them apart from others who are using the default avatar.
Unlike the other sets, which are more whimsical, it would be nice if there was a more professional option besides the Mystery Man. Ideally, the generated colors would be muted a bit (grays, light blues, light greens, light reds, etc.) so they do not contrast with the sites and are not too overpowering. For example, a bright magenta avatar might not look that appealing. Also, since people can't choose their colors, neutral colors would be the best option. They can always register a Libravatar or a Gravatar if they don't like the color, but we should probably avoid outrageous colors anyway so it appeals to the widest audience.
Thank you for your time.