It has certainly has been stated that LinkedIn is for adults. But like any two products in a category, they each have there own persona.
- LinkedIn makes its money capitalizing on the age-old adage: "It's not what you know, but who you know."
- MySpace makes its money reaching a key demographic: "It's not what you know, but who you are."
Originally started with executives in mind, LinkedIn has moved 'down-market' as it grows to an estimated 10 million users by year end. Originally started for adults (but not adult content), MySpace has proven attractive to younger audiences with its 100 millionth account created this summer.
The odds of overlap are pretty small in absolute numbers (no more than 10% of MySpace could have a LinkedIn profile.) Of my extended network of 1mm+ LinkedIn users the phrase "MySpace" returned only a couple of hundred people. Now I'll admit many may not cross-post in order to separate their after-hours life from their day job.
[UPDATE] - Age profile of MySpace getting older. Half of the users are over 35, up from nearly 40% last year. So, is the brand diluting?