A brief description is a sound idea, I'll need to keep it very brief if I'm going to cram in other link buttons as well.
It's nice and is commonplace to have social network and subscribe banner buttons however there are standard channel subscribe buttons and social network links on the channel page anyway so I'll see if I can think of anything different to that. It definitely improves visibility but I just feel there is little bit of redundancy there but like I said, it's a common practice with banner designs to have those buttons in addition to the ones on the sidebar and standard channel subscribe button.