I've always refrained from implementing both comments and Trackback on my sites for two main reasons: lack of maturity in some segments of the overall populace (i.e., some people are fundamentally uncivilized and unable to carry on a balanced discussion), and Spam. And leaving my Wiki open to the outside world inevitably results in some idiot posting BitTorrent links or some such childish nonsense.
As to authentication, I've looked at TypeKey to authenticate comments (and Wiki editing) more than once, but in my opinion it's simply a matter of time before any Web-based authentication system gets hacked and goes to the dogs (cases in point are Microsoft's Passport, Yahoo's account sign-up forms, etc.).
Throughout the years, I've found E-mail to be a much better way to receive feedback - people tend to be much more responsible and come through in a less superficial way through it. And, of course, SpamAssassin takes care of the usual idiots.
Supporting Trackback also involved paying attention to pings and whatnot, storing the results and formatting them - which turned out to be too much trouble. With HaloScan I can remove either comments or Trackbacks in an instant, get a simple RSS feed of comments, and don't have to code anything.
So I'm going to see how it goes for a while - if I find the results encouraging, I might actually stick with it.