In the process it serializes the threading and so it's going to destroy the threaded nature of these reposted conversations. In this way it's rebranding the information served here, misrepresenting the attention commenters here give the post, and confusing the outside reader.
I know there's an attempt to smooth these difficulties with the "This comment was originally posted on [[Hacker News]]" line but that leaves me still confused as to the origin and meaning of the comment quoted. I interpret that to mean, ridiculously, that commenters at HN gave their permission explicitly to repost comments on Feint. Actually, it even appears to me that they personally moved it.
This is, of course, very similar to the the controversy AllThingsDigital stirred up a little while ago (http://waxy.org/2009/04/all_things_digital_and_transparency_...) but I don't think Feint is really making a large improvement over that situation.