I don’t get it! Why should I need to sign up for username on an commenting system/networking site (whatever you wanna call it), just so I can come back and comment on your site? Is it to control who’s leaving comments or is it a numbers game? To me it is more of annoyance.
What is wrong with the simple already user-friendly comment code that is in your blogging platform (ie. wordpress/blogger) already.
/end of rant!