I find it absolutely obnoxious that the first time I hit "Preview" in a Reply, the software collapses all the spaces between paragraphs, making the post unreadable. I have to go through and fix them all manually. After I fix them, they stay there after hitting Preview or Reply.
I also liked the limit on the number of downthumbs or upthumbs people could give in the old forum. Now people can go around stalking others and downthumbing every post of theirs. Nado, LoT, and bosco do this to me, for instance.