Just for information. Model-First Data Migrations does not work in VS2012. This is when you need to the update the DB without loss of data. This was provided by the excellent "EF Powerpack" for VS2010. However this is not supported in VS2012. I
have contacted the EF Team about this, and it is a known issue.
Since I use this, I have to stay with VS2010, and hope they resolve it shortly.