On board motherboard sound has dramatically improved within the last year and now we are on the verge of seeing motherboards with the ENVY chip for sound.
The ENVY chip is used in higher end PCI based sound cards.
You got to divide the market into two parts to get a better understanding of where the impact will be. The "off the shelf" or DELL buyers represent a very large segment of the marketplace....extremely large. THey are buying on price point and options. Most just know how to turn a PC on and that's it. So the impact is less as the consumer just doesn't know the difference.
OEM buyers like us are picky. We do recognize that on-board sound has really improved. But it still isn't as good as PCI based solutions...so at this slice in time...no...there isn't much impact but there still is a bit nonetheless.
This, however, may change once the ENVY onboard chip comes out. That does bring the promise of PCI based audio card quality onboard.
Which may have the impact of brining even higher end, more expensive sound cards down in price.