I think everything has been answered already. The version available now lacks the PS2 BC, only has two USB ports, and had the card readers removed. They update it every so often improving video support and adding new features. The media server capabilities is a great feature that i've found useful. Also, the option of swapping the HDD for any other 2.5 inch drive is a plus. Unfortunately, most games require an installation before playing, sometimes up to about 5GB in size.
There are rumors out there that a slim model might be coming in the near future. Nothing's been confirmed, just a photo of a possible box art and a piece of the system. If it's true, they wouldn't confirm it until the system was prepped for release anyway.