Before you migrate, one thing to consider is that the 3.0 Community Edition has fewer modules than the 2.1 Open-Source edition. While upgrading should be as simple as uninstalling 2.1 and then installing 3.0, you may lose functionality that you currently depend upon.
Please refer to our product matrix for a list of features that are not in the Community Edition.
http://www.splendidcrm.com/Products/CompareEditions/tabid/121/Default.aspx