The problem with cartridge bearings is that in order to get the extra cartridge bits to fit inside, the bearing itself has to be shrunk. You end up with tiny balls taking the load and they end up having short lives (think Octalink bottom brackets, which have exactly the same issue). The better-designed cartridge headsets are OK (think Raceface Real Seal, Hope etc) - look for one that looks rather bulky; but the cheap, light, dinky ones are not great.