Just throwing in my two cents, but I wouldn't bother with grades. If you want to teach, or play on the classical circuit then yeah, its worth doing becasue it amounts to a professional qualification, but if you're just learning for your own pleasure or to play in bands you're probably better concentrating on playing what you want to play and becoming awesome at that rather than learning a bunch of pieces for the sole purpose of getting a certificate.
Of course, some people like to learn that way. Having an exam to work towards can keep you focused and on track so if that's the kind of learner you are then by all means go for it, but persoanlly I can't imagine anything worse than learning to play your insturment that way.