Maybe you could write a Greasemonkey script? You could have randomly generated avatars like Miis. Then you could also assign an image for specific posters that you feel are better indicative of their personalities.
I'm not sold on the idea of something like this here, but even a very small icon (like 16x16 or smaller--very small) or bullet of color would would make threads easier to keep track of.
The only problem with identicons I have seen is that the algorithm used causes a majority of them to look like swastikas. But that seems like an easy thing to fix. Most of the identicons are quite pretty (including a large number of swastikas), but most people still associate swastikas with naziism.
Swastikas aside, I don't personally feel they're a good solution. They can be useful in semi-anonymous situations to determine one person from another (or an impostor posing as someone else), but I don't find them even vaguely recognizable from one another in the most case. They're very easily confusable.
I think the human brain is optimized for recognizing faces. Those geometric variations of identicon don't look different enough in my opinion. I like the general idea, though.
If the purpose is -- as you say -- to "start associating usernames more with their set of comments", then random images should suffice. If the purpose is to have a visual item of personal expression added to each post, I suppose you'd need each person to choose one for themselves.
Well, a random image may not suffice for that purpose. I just don't know. Maybe for it to work, it has to be some sort of recognizable image. But random images would at least be worth a shot.
