Google talk team has come up with a talkback gadget which can be added to your site or blog. This will allow visitors to be able to chat with you on your gtalk account if you are online. With just few lines of html code, you can be now be contacted from anywhere on the web. The interesting catch is that the visitors need not have a gtalk account or even a email address to be able to ping you.
Update: I have added this to my blogspot blog and also to my wordpress blog using a trick as suggested in this blog http://daniel.fallenste.in/2008/05/18/howto-google-talk-badge-on-wordpresscom/
Cheers to Innovation @ Google.
P.S Am not too sure if this is a original idea by google, but then what ever google does will have a massive usage and awareness.