Here is an interesting infographic from web analytics company Compete that explores the income breakdown of the user bases of six top social network, including Pinterest. Much of this is probably in line with what you thought the breakdown was for each. Google+ skewing wealthy is a bit of a surprise.
What I do find interesting is how balanced Pinterest is. Pinterest seems to really cut right across all earning levels and have a very even distribution. Regardless of a person's income level, they can still have fun finding stuff that they either want to try or wish they could try and sharing it all with the community.