yes I think it’s all about just making things easier for people. Social network websites seem to thrive on low attention span activities (and for the web, that’s going some). ‘Would you like to join these groups?’ with a 1-click purchase option ( 😉 ) seems a good one. Emailing people on my contacts list the longwinded full hyperlink to the Hertfordshire page was a non-starter.
And yes, these circle things may turn out to be just a gimmicky selling point for the Google Empire to try and poach people from other social networking sites. (evanescent Gwaves –map to–> inward vanishingGoogle+ spirals??)