This is useful for Gmail power-users who don't like trawling facebook - basically pulling all the social info you have on someone from twitter, linkedin and FB into the bit that used to have the Google Ads. Perfect. And with added deep FB integration so you get all sorts of info.
Also helpful if you have problems knowing who the person emailing you is. I was anxious about the idea of giving access to one app to all these sites but the security issues is dealt with by OpenID so it also feels relatively secure(!) At least Chewy and RWW think so http://goo.gl/FI82 - which is enough for me. http://rapportive.com