i don't know what firmware you get when u buy a new ps3, but it's probably 3.41, 3.42, 3.50 or below. you can only jailbreak a ps3 with firmware 3.41, but if you have 3.42 or 3.50 you CAN downgrade your ps3 to 3.41.
a ps3 with 3.55 is NOT hackable yet, but as there are private keys and stuff released, there will be a custom firmware soon, so there's no need for jailbreaking anymore
and buying a ps3key is pretty much waste of money right now. only jailbreak if you have an iphone or ipod touch 2G is something to do it. otherwise just wait for those CFW's