Here's what Mel said during a TV interview:
"Yes, 2012 is a long wait, but I think it'll be worth it. I need to make sure it's the best it can be for all my fans, and I want to include the moments which were really special for me throughout. 2012 is an approximate date,and we may release it sooner. Fingers crossed, everyone, and I'll let you know when there's more info!"