Chat privately with visitors on your social network profiles, blog, or website through Yahoo! Messenger.
Yahoo! Messenger Pingbox™ 
Create your pingbox, style it, copy the code and paste it on your blog. Only you and person you are chatting with can see the IMs, even if there are multiple visitors viewing your web page. Sign into Yahoo! Messenger and receive private IMs from your visitors. It’s that simple. Read More>>
For me, this is one of the bestest features introduced by Yahoo!. It looks amazing on my site. And members love it. I really find it very convenient and fun to use.
I hope we see more features soon to integrate it further with a site so that logged in member’s username can automatically be filled in the “nickname” field.
Also this has a compatibility issue with Google Chrome which should be fixed asap.
Thank you