Good as in you want protection from dropping or enough to protect it from being scratched while you carry it around? If it's the latter, i've bought 2 sleeves before (1st for my MBP, now for my MBA) of this:
Having a spot of difficulty following the logic of spending the coin for a first class, best in the business laptop and protecting it with the cheapest, presumably least effective sleeve. But, whatever floats your boat.