Here is what i found at Yahoo answers….
a social butterfly describes a certain type of person that fits in with pretty much anyone they are surrounded with it doesn’t matter which clique or whatever you want to call it they are in or talking to. they are easy going, out going, and talkative, and can make conversation with just about anyone.
According to Urban Dictionary social butterfly means
It’s a word/title that is usually used to describe someone that is popular. Often times those people are friendly or pretty, but it is not always the case. It is not always used to describe popularity alone, it could also be describing someone who is friendly to strangers. Typically a word used to describe females.
Someone who is VERY social and easygoing; can be either a male or a female. Usually these people don’t belong to a particular group, but rather jump from one group to another. They are somewhat accepted in all of them, but don’t really have any deep friendship connections in any of them.