I have recently added support for coComment to my blog and it was extremely easy to do. After signing up for an account, I simply added the following code to my Add Comment Form Document template:

[script type="text/javascript"]
var blogTool = "DominoBlog";
var blogURL = "[$DXURL$]";
var blogTitle = "[$DXTitle$]";
var postURL = "[$DXURL$]dx/[$DXDocumentLink$]";
var postTitle = "[$DXSubject$]";
var commentTextFieldName = "textcomment";
var commentButtonName = "SubmitButton";
var commentAuthorLoggedIn = false;
var commentFormName = "_DominoForm";
[/script]
[script id="cocomment-fetchlet" src="http://www.cocomment.com/js/enabler.js"][/script]

Of course you need to replace the [ and ] with < and >, but that's all it took to make my site part of another Web 2.0 community.

UPDATE:After finding an issue with my own site, I have made a slight change to this method. If you are using linline comments, instead of adding the code to the Add Comment Form template, you should add it to the Document template directly after the $DXCommentForm$ tag. If not, the DXSubject and DXDocumentLink tags are not replaced correctly.