Tablets and smartphones will be overall additive to Intel's revenues, because we are not going to see a 1:1 replacement of a laptop/desktop, with a tablet or smartphone.
Tablets replacing PCs is already happening. That's why Intel's sales are slumping. Now, it won't be the entire market, but it would be enough to cause serious problems for Intel if they don't get a big piece of the tablet market.
Intel doesn't have the quasi-monopoly of x86 patents to fall back on. That's their problem really, and probably why they still continue to push W8 when it's already been rejected by the market.
I expect in time that Intel's Atom SoC's will lead on performance/watt over its ARM rivals and too many people don't understand that if a $30 chip has a good margin in it, then it doesn't matter that it is only $30, unless it is directly replacing a more expensive chip.
I'm still very skeptical Intel can make the margins work, especially with their costs so much higher than everyone elses. And that's if they can even get into Samsung or Apple, which isn't a guarantee.
Also keep in mind tablet ASPs continue to tumble. Apple hasn't announced their results yet, but reports are the Mini is selling very well ... at the expense of the big iPad. This should pretty much end any hope that Intel had that expensive tablets would be sellable.
