I don't consider x86 as a viable tablet solution, simply because of the reality of power management and performance. Don't get me wrong, I think x86 embedded systems are a viable solution for some scenarios (I use an AMD geode board as a dual radio AP/media box/thingy in my Jeep and another one as an AP at the house), mostly due to the fact that they're much more efficient both in size and power consumption than a full PC, but they're certainly not on the scale and power levels of the ARM boards. Quite frankly I think the software discussion is a mute point, as any handheld device is going to require at least some level of software customization in order to best suit the needs of the user, and any well written code should be portable enough to translate between x86 and ARM without a lot of difficulty... the argument for x86 here is really more of "an easy way out" than a real solution to the scenario in question, and at the end of the day the quality and performance will suffer as a result.
It's interesting times definately for this stuff, especially with the latest omap3 chips... In terms of tablets, I strongly believe Omap is king, hands down. In terms of general embedded devices, it's still more of a gray area, more dependant on the costs and features of given boards and systems along with requirements than with chipsets.