When you open a pre-R2009 sheet metal part, all of the parameters and options that were used to create the part are retained in the migrated part as local styles. Each of your sheet metal parts before R2009 may have been created from a single template with a comprehensive set of material thickness definitions. Saving collections of: materials, thicknesses, bend, corner, flat pattern options and unfolding preferences to named Sheet Metal Rules and Unfold Rules in a global Style Library may ultimately provide you with more efficiency and flexibility.
You can continue to work with your legacy sheet metal files migrated to R2010 without moving any style information to a global Style Library. Legacy style information is maintained locally within the migrated file.