I know this probably been talked about a few times, and YES, I do know that you cant share the minecraft.jar file, because it's copyright and all, but I have an older Mac OS X laptop with 10.5.8 (Leopard), I cant get all the good programs that others can, not even InsideJob, a minecraft item edit program. And, I've use up quite a bit of download limit JUST, yes JUST, trying to get the Minecraft Single Player Commands. Its pretty unfair, and I've complained to my mother about this laptop of mine, and she just says: "Your going to be in year 7 next year. Wait until then (which, mind you, is in over half a year, and i'm in australia) play around with your Minemaker or whatever its called."
I hope you just have a THINK about it, to everyone who sees this, dont start giving me crap about complaining.
Remove that awful Mac software. Load Ubuntu. That will solve pretty much all your problems. MacOS is simply a freeware platform of linux (yet they release a new one every year and make you pay for it. Funny huh)