I'm really disappointed at this product. Not only does it require THREE separate parts to work (ExpressCard, the adapter itself and the Thunderbolt cable), you have to buy the TB cable from Apple. That means you're paying nearly $300 AND lugging around 3 components. Definitely not an elegant nor financially practical solution at all.
I'm looking forward to the day that we see a Thunderbolt to USB3.0 + FW800 hub for less than $200. That I'd buy in a heartbeat.
I would imagine there will be several ripoffs in the next few months. I was thinking It might be wise to wait for some Ebay deals from China. They may resemble sanity at some point.