I haven't used carpet on top of carpet, but I certainly see it a lot any more...a decorating 'fashion' statement. I've vacuumed at my SILs though, and I don't like to fuss with the edge around the area carpet placed on the wall-to-wall - so chose not to do that here in my living or dining rooms which have off white wall to wall carpet.

If you are interested in trying it without investing lots, several on the home decorating forum here have suggested esalerugs.com. That company was new to me but most seem to have been pleased. At the recommendation from posters there, I've just now ordered poly runners that have the look of oriental rugs for the hallway through my mudroom and the far end that leads outside to the patio. They are telling me can be hosed off if they get especially dirty....we'll see. The rugs aren't due to be delivered until mid week next week so I can't speak to their quality first hand.

Thanks for the tip for esale! Prices look fantastic! Would love to hear about your opinion on their quality once you received them.

one4, the runners/rugs were delivered today and I'm pleased with the quality. They came just 7 days from ordering too, pretty speedy considering they were sent from North Carolina to coastal Washington state.

They are nicer than I expected for no more than I paid. I wanted something bright and welcoming for that mudroom hallway and they are true to color, nice tight weave to the backing. They came rolled, back side out, and one end on each doesn't want to quite relax immediately out of the packaging, but I've rolled them in the reverse and will give them a couple of days. Overall, I'm pleased - they are prettier and better made than the two dark brown Home Depot runners I've had in that hall..... Purchased two of these, so not their better rugs...

http://esalerugs.com/red-8-ft-runner-mashad-design-area-rug-33124940