This implementation by Facebook does have a "Post to Facebook" checkbox for whether to also post the comment into the user's stream (making it potentially visible in their friends' streams), so in theory people may uncheck the box and you'll lose the viral aspect of the comment - but you'll still have the comment on your page, and others may well respond to that.
Using Facebook's comment system may be regarded by many as a sell-out to get a quick fix and a bit of viral looping within Facebook, and the only long-term winner here may well be Facebook as it becomes more relevant to ever-increasing portions of the web. Others may regard it as a natural, no-brainer way for small sites to get a foot-hold on the social web.
Whatever your own view, it is certainly easy to implement. The code looks like this:
<div id="fb-root"></div> <script src="http://connect.facebook.net/en_US/all.js#appId=143241589035224&xfbml=1"></script> <fb:comments href="swinny.net" num_posts="100" width="500"></fb:comments>
Note that you need to have created an app within Facebook, and made sure that the app has its Site URL and Site Domain filled in correctly.
The details you need to have to hand are: