I'm a diehard Apple guy (unlike my friend Steve), so HP's new Slate 500 is less than compelling to me. I'm old enough to remember the early Windows-based tablets that never really worked, since the OS was designed for a keyboard and mouse, not a stylus. Now we have the Slate, which is based on the much-better Windows 7 OS, but still was designed for a computer, not a tablet (ie. something you control with your fingers).
I'm sure, like the old Palm Pilot, that developers will design specific apps for it, but at first glance, it looks like general consumers would be better off with a generic Windows laptop. As for me, I'm taking a look at the new Apple MacBook Air, especially the one with the 11-inch screen (I already bought an iPad for the office!)
What sets the iPad and the Mac laptops apart is that their software has been customized for the hardware...it's been this way since 1984 and unfortunately, many Windows devotees just haven't had the opportunity to experience this seamless connection between software and hardware. If you try out an iPad, you'll see it doesn't work like a laptop, because it isn't meant to do the same things. It's primarily designed to consume media like movies, books, magazines and TV shows. Sure you can email and surf the web, but you'll be much happier creating content on a laptop or desktop computer.
As for the Slate, I don't think you'll be happy at all.