Yes! Upvotes/Downvotes would be really helpful in discussion threads, as rather than everyone having to list their individual opinions or quoting and seconding other comments, we can easily localise our input, and give an overview of which opinion is most popular with users. I think it would be especially useful in this suggestions thread, as there is no way to see what the majority opinion is on sub-suggestions, and if one person's additional input is a good idea that the community will like.
Also, it's just frustrating when I go to like someone's comment, and I can't. ^^
