Buying it now is certainly not a bad decision. It's an awesome phone. Just be prepared for the possibility that it won't get ICS (it's not a guarantee either way). As far as Cyanogen support, the international Galaxy S is not supported, but some localized versions (IE, Captivate) are.
I agree with you on many custom ROMs, but if he wants ICS support, and there isn't an official relase, Cyanogen is a fairly close to vanilla option.
