I think the future is a more powerful lightweight notebook with a detachable touchscreen. People are making it all look like these either/or choices but it seems like technology is clearly converging on this happening fairly soon. Already there are quad-core tablets now being released. Think about what is missing from a tablet that makes it more powerful: more storage, more RAM, slightly higher resolution screen/better graphics, and possibly more ports. All of these should be possible either with current technology or in the very near-term future with the progression of technology in areas such as flash storage and improving compact design.
Turn it the other way around and look at what makes a ultra-portable laptop a bit still a bit too much to just easily throw in a purse and take with you - battery life not that great, hard drive - even if SSD - is still too bulky - basically whole thing is still too heavy to really be ultra portable.
From either perspective there is definitely convergence occurring so considerations now about which is "best" are more matters of personal need/preference.
One of my longer-term concerns will be, whichever platform is running, that there exists graphic or other software for it. For the time being Android and iOS might be safe but when the technology allows full-blown Windows to be on devices lighter than a pound then MS might be set to make a killing.