CRM 4 Mainstream Support – Why haven’t you upgraded to CRM 2011?

Only 6 months left for CRM 4.0 Mainstream Support which will end on April 9, 2013. Isn’t it time you upgraded to CRM 2011? In a few short months it will have been out for 2 years.

What is the difference between Mainstream Support, Extended Support, and online self-help support?