This is a pretty good video about Agile estimation and planning. I recommend it is worth a watch. Its very interesting at the start where lots of people in the web conference put in there comments about planning.
And there is a great point made at the start of the video. That goes something like this – ‘At the start of a project when we know least about it, why do we plan so much!’ This is why Agile emphasises managing change over planning.
The video is presented by Sally Elatta, president of Agile Transformation Inc