Renovating a kitchen - I have pulled down the cupboards and bulk head, in some areas the new cupboards will not cover the drywall damage on the walls and ceiling. The old cupboards show bare drywall. Can I skim and repair these areas, or is it best to replace the drywall sheets?

Depending on the type and extent of damage... its usually easier to replace the sheetrock in its entirety.

By the time you patch and patch and sand, you can replace. Drywall is $7 and you will spend more time patching.