After using regular SanDisk Memory Stick Pro, I indeed noticed read/write speed improvement: about twice faster, I would say. SanDisk uses same Sony memory chips as Sony does, they just package them on their own factory, so theoretically you are getting same product with different labels. So why pay extra for "brand", if you can get same product with lifetime warranty anyway?
If you are considering this card for your digital camera, do not set your expectations too high: though you are gonna notice that Ultra-II' write speed doubled over regular cards, the real bottleneck is your camera's shutter lag and size of the camera's internal buffer (in burst mode). In auto-focus mode, the lag on my Sony DSC-717 is still over a second - I'd say about 20% improvement. If you want to shoot faster, learn to use manual focus.