I saw no negative impact on forums I watch.
Ascension, I disable the "quote" button on forums I'm responsible for. That's not because it's bad for SEO (it surely doesn't help), but because heavy use makes a thread much harder to read. It's all too common to see someone include five paragraphs of redundant text in a two-word post.
It's an interesting thought that on-page redundancy could be a factor in Panda results.