The hack works, we've seen it with our own eyes. And you can order it for $99 now in the US, or less than $50 from Australia. But the fulfillment process isn't live yet, according to the Wireless Imports, the only US-based retailer of the hack: "We are awaiting to hear from them later today about when we will be able to start unlocking handsets." The Australian Retailer says the same. Even though IPSF has proven itself beyond any doubt, I'm going to say wait a little while before buying.
Unlocking the iPhone is important in principle, but unless you MUST HAVE RIGHT NOW, I'd advise that you wait a few days before plunking your cash down; iPhone Sim Free folks have been verified as legit but we don't know what will happen to the hacks when firmware version 1.03 comes out. (They aren't guaranteed as future proof.) At the firmware update, we'll be able to tell at least what Apple's will is toward the unlock, hostile or neutral.
Also, the $99 and $50 prices out there show that the market hasn't settled at all. I'm sure it'll go cheaper than $99 very soon, given the nature of competition. I'd say that an unlock that is future proofed is worth about $50. What do you think is a fair price?
Lastly, even though iPhone Dev Team won't reverse engineer the hack (according to good source within the iPhone Dev Team) out of respect, they will continue working hard to do this for free on their own. Can you wait for that to happen?