Small suggestion: Mousing over the red envelope could tell me how many new messages there are.
Medium sized suggestion: A "what links to this?" button on posts.
Big suggestion: A search feature that only returns hits on posts, comments, and wiki pages, sorted by date or karma, filterable by author.
Multiple envelope images:
gray = no messages;
thin-lined red = 1-4 messages;
thick-lined red = 5-9 messages;
very-thick-lined red = 10-19 messages;
almost a filled red rectangle = more than 20 messages.
I think it'd be a good idea to keep a list of the ways we'd like to see LessWrong improve, sorted by popularity. Ie. email alerts for new responses.
So if you have an idea for how LessWrong could be better, post it in the comments. As people up/downvote, we'll get a sense for what the consensus opinions are.
I think there's a pretty good amount to be gained by improving LessWrong.
Note: I say "ways to improve" instead of "features" because "ways to improve" is more general.