Twitter Circle, a new way to Tweet to a smaller crowd

"With Twitter Circle, people now have the flexibility to choose who can see and engage with their content on a Tweet-by-Tweet basis. This makes it easier to have more intimate conversations and build closer connections with select followers."

The best feature from Google Plus comes to Twitter. Hopefully they will allow users to define multiple Circles for different types of groups, e.g. Family, Work, Hobby, etc.