Just picked up the Samsung ATIV 500t. The dock is a bit disappointing (requires you to really push it in to stick, otherwise it will dock/undock a ton -- also no battery) but fanless + wacom support tipped it over for me.
After playing with it for a while I am having a hard time believing ARM tablets will succeed unless the pricing changes in a big way. Unless they can compete on price, next-gen atom will sweep the market. On the price competitive not though, they were selling the ASUS VivoTab RT for $399 @ the local Microsoft store. Not bundled with the dock, but ASUS will give one to you for free. Almost bit, but how many tablets does somebody really need?
If they can get to the point where decent ARM-based tablets are in the $299~$399 range I think they will be strong competitors. Otherwise, why bother? That being said, while I was not a hater of Windows 8, after using it in a tablet it is like a light went on in my head. This thing makes other tablets feel like overpriced toys.