I wouldn't say useless. Its "uselessness" is the same as any other technology, be it cell phones, computers, or the internet itself. It really boils down to how people use it. Some people waste thousands of hours in front of gaming consoles. Others chit-chat on their cell phones all day long about nothing. Some people will use the Surface for entertainment or useless things, other will be creative, inventive and/or connect to the world with it. I think it looks cool. I would buy one if I was rich.
Let me qualify what I said...it's about as useful as an XBOX. At least cell phones serve a useful purpose of connecting people. There's nothing that you can do with that table thing that you cannot do with a computer. Even if I was rich, I would not buy one. I would instead invest the $10k or so to make more money or donate part or all of it to MPrize / stem-cell research.