How many concussions has Sidney Crosby had?

[evevale]

I'm having a conversation with a couple hockey friends of mine and they were talking about the whole Sid vs. Alex "rivalry". One of them argued that Alex is more durable which makes him more productive. I've only known Sid to be out for an extended period this season which is a shame because he was playing so well leading up to the concussion.

Which leads me to the question, how many concussions has Sidney had in his career and when is he expected to return?