Prior to CK's acquisition by Rackspace, I'd say the main selling point is a common control panel experience for cross provider stuff. They were adding on monitoring as a pay service top as well.
I was suggesting it initially as a way to not suffer any pain with the existing Rackspace Cloud CP.
What's the draw for using CP on Linode? I'm completely happy with the Linode control panel experience.
AWS I don't have to worry about because I use DotCloud which handles all my network configuration and instance maintenance.