Well, I personally think that my LJ is something special, and I want people to be able to read it if they wanted to. So yes, an LJ button would be nice.
Except, we can't just lmit it to LJ, so make it a "Blog" button instead. I guess you could put it with the other buttons at the bottom, but I think it would go nive a bit bigger and on the right side with your post count and stuff.
Trying to sell my LJ in my sig takes up space where I could put other funny random stuff anyway. I second the suggestion.