First off, let's deal with the little problem of "special" characters. I've seen users try to post in Japanese before, and fail (see Tsukasa-Hiiragi's comments here), and I, personally, once tried the "reverse text" formatting character, with disastrous results. So yeah, it would be cool if NG allowed more "special" characters, rather than limiting to just the usual plus a few accents.
Also, I thought of an idea a few nights back that would be pretty cool... Why not have changeable CSS? Now, hear me out here: wouldn't it be cool if someone could go into their account and make NG look like classic NG, YouTube, MySpace, 4chan, or other popular sites? I don't exactly know how that would work, but I do think a lot of people would at least use the NG Classic style.
Also, public ban messages, as a way for a mod to show the userbase what is and isn't bannable. Just an idea I ripped from the imageboards... It would help to keep users, at least those who didn't want a smack with the banstick, in line, by teaching them what kinds of posts are and aren't ban-worthy.