I, like Abstract, assumed that FF would produce print qualities better than the APS at the same MP rating, that's why I leaned toward the 5D with it's L series kit zoom lens (less than $3k at B & H). I assumed that the kit lenses on the APS's were of lesser quality and that even the "pro" lenses mated to an APS would not match a FF with good glass.
That's not correct: having a larger sensor size also means, you have to make trade-offs that reduce image quality. So usually you will not have better IQ with a larger sensor and a (compared to pro glass) mediocre lens.
Assume we have two cameras with roughly the same MP count.
Larger sensors will then give you larger pixels and better noise characteristics -- which is
only relevant if you shoot high ISO. If you shoot at ISO 100 or 400, practically you will not see
any difference in terms of noise. That's because noise is so well controlled these days.
The second point is that all crop sensors have the so-called sweet spot advantage.
Any crop sensor benefits from this. Any lens has defects and some characteristics dictated by physics (e. g. vignetting and fall-off). The further towards the edge of the image circle you go, the worse things like sharpness get. Crop sensors don't see the regions where sharpness and falloff is worst (the edges of full frame), they are in the `sweet spot' of the lens. This is no longer true with the 5D or any other full frame camera.
For example, there have been comparisons of the Nikon D2Xs and the Canon EOS 1Ds Mark II where they have compared the effective resolution (i. e. the resolution as measured from the image files produced by each of the cameras). Surprisingly, the D2Xs won up until f/5.6, although it had a lower MP count. This was due to the sweet spot advantage. (They've used macro lenses, so they've actually measured the camera + lens combo.)
IMO people should be pragmatic about it. Although I would really, really like to have a D700, there is a snowball's chance in hell that I will be able to afford one in the near future. Lenses are much more important, because I'd rather have three decent lenses and a camera with a crop sensor rather than one lens and a full frame sensor-based dslr and a big hole in my bank account. Full frame sensors
need very good lenses (which usually are very expensive), otherwise it's like slapping $50 tires on a Ferrari. Otherwise, they will not give you the improvement you were hoping for.
To get back on topic, I've made large prints (roughly 30x40 cm^2) of even 3 , 4 or 5 MP pictures and they look fine on the wall. Of course you
will see pixels if you get glose enough. But they are on my wall, they are very powerful images (at least to me) and no one I've met told me `well, look at the pixels!' I've also had 10 MP and 12 MP pictures printed. The 12 MP picture was printed to roughly 50x90 cm^2 which looks very good, too. The big one now hangs in my parents' living room, I gave it to them as a birthday present. Don't worry about MP and large prints, today's dslrs are definitely up to the job (unless you are a professional who needs the absolute, absolute best in terms of quality).