The PRO-HG Duo HX debuted last summer with a read speed of 20MB/s and a write speed at about 15MB/s. That write speed looks like it will remain, but the read speed has been bumped up to 30MB/s.
This should make a huge difference when it comes to transferring large files like high-res photos or HD video clips. Sony provides the example that a 30GB full HD video file can be transferred to a computer from the camera/camcorder in about 17 minutes.
The Memory Stick PRO-HG Duo HX is available in three capacities (8GB, 16GB and 32GB) with prices starting at $59.99. Be sure to pay attention to the product description if you're planning to buy one of these cards soon as the old 20MB/s versions are still on the market, and the updated speed probably won't be available until the next production round this summer.