I did this in my house when we added a second floor several years ago (not a huge house - about 25' deep x 40' wide with a full basement under). This was before the consumer integrated systems were out, and I've felt no need to upgrade. We have a fairly tight suburban neighborhood; I can see 15 other APs (a few poorly configured at the moment, alas).

I hardwired a couple closets with Cat 6, both situated about halfway between the front and back of the house. I put a PoE AP in each, both running 2.4 and 5 GHz simultaneously, all on the same SSID - so four channels total. One is on the first floor at one end of the house, with the AP mounted high on the wall facing inward. The other is on the second floor (about 13' from the other end-wall) with the AP on the ceiling. I've found nothing close to dead spots, and my teens and their friends comment on how much better our wifi is...

The only thing we don't have is seamless handoff when streaming video on portables. Haven't really missed it, though; I tend to pause streaming when I'm walking around.

-jk