From what I can see, nothing. Sure, Moore's Law means that they will be faster and have more storage than their predecessors. Battery life will also be better, as will screen resolution. But these are evolutionary betterments as opposed to revolutionary leaps in thinking. Ultimately Slates are the same as the Tablet PCs and UMPCs that came before them - a PC running Windows crammed into the TV part of a desktop system (I'm using mass-market lingo here), then the whole thing miniaturized until it's portable. Same thinking, just a different operating system.
What's important to realize here is that the iPad has been a success for Apple, but Apple didn't start out with the idea of miniaturizing a Mac OS X system down into a tablet, but of scaling up the iPhone. As elegant as many seem to think OS X is, on a tablet system it would be no better than Windows is, partly because the OS wasn't designed for tablet use, but primarily because OS X applications, like Windows applications, are designed to be driven by a keyboard and cursor, not a finger. Adding a stylus to a product only underlines the fact that Windows doesn't work on tablets. OEMs might as well bundle a keyboard and mouse with each Slate.
Even if Microsoft tries to blow smoke over the issue that Windows doesn't make a good tablet OS by starting to talk about Windows 8 and possible tab let customizations there, this still doesn't solve the problem that the main reason people want Windows on a tablet is to run Windows applications on the tablet, and Windows applications are a big part of the problem why Windows-based touch systems don't work.
Tablets and slates have a future, but I see Windows-powered Slates failing to jump Moore's Chasm, just like Tablet PCs and UMPCs failed before.