I used to really belabor similar things in the audio world. As a result I did extensive mods to my A/D/A, built custom preamps, did vacuum tube implants in studio microphones, all kinds of crazy stuff. And it all did in fact make improvements for the better.
Ditto, I built my entire sound system (speakers, amp, tube turntable amp) instead of buying, to get something sounding good, then I just conveniently ignore all the dirt making pops on my vinyl (and don't bother washing them)...
Back to cameras, I've tried PanoTools for de-barrelising, i've tried DPP's auto-vignetting and CA corrections.
None of them I use any more. Not that i'm lazy (although there is a bit of that), I'm just being realistic. So far I've only printed proofs at 4x6, soon i'm going to print some 8x10 pics of my missus' sisters' dog for her xmas present, and I doubt i'll see any CA or noise issues in anything that size either.
As I wrote in the 7D thread, it's all about expectations.
Someone moving from a 5D2 to 7D might hate it for IQ, or they might love it for the AF, FPS, or other features.
Someone moving from an xxxD, point and shoot, or film might love it, or they might ignore all the other good features and concentrate on one negative, like noise.
Some people won't be happy with an IQ180 and Schneider-Kreuznach or Zeiss glass, because for the price they've expected a lot more than it could have been.
Not saying that this is what friedmud is doing, he came with a question that I interpreted as "is this normal or a dud?", unforunately I haven't processed a RAW from his camera in my workflow to be able to comment on that (and the thread seems to have been hijacked in parts by people with strong opinions regardless).
There's always going to be semblances of "a poor workman blames his tools, but moreso, there should be "the right tool for the job".
I bought my 7D as my first dslr, and my 2nd digital camera (8mp olympus u820 came before), mainly for price. I took a month deciding between it and the 5D2, I went for the 7D and 15-85 with 70-300, otherwise I would have only gotten the 5D2 and 28-135 or something. Only after I bought it did I discover how much I liked birding, which is probably one of the best uses for a 7D.
I accept that there's limitations on using it for landscapes, astro, long exposures, low-light, etc. I still use it for these, but I'm not going to go into business selling star-trails, it's for my fun only. I will get a FF one day, maybe only even a 5D or 1Ds2, or even film (i'm planning on a film-Medium Format before that though).
(Coincidentally, I've been unemployed for 6 months and more and more people are telling me that I should be a pro-photographer for a living. It's hard explaining to someone that I've spent $5k on equipment that I wouldn't even think once about shooting a wedding or concert with. Even when they see some samples I show of concerts I have done for fun, they just don't see the noise or other limitations that I do).
I've got a friend who just got a 550D and 18-55IS. He's taking shots already, that I would have loved to have taken, he's got a very good eye for things, and he's certainly practising like crazy. He isn't pixel-peeping (probably doesn't even know what the term means), he's looking at the big-picture (both literally and metaphorically), his composition skills are great already, I can see him becoming a good street-shooter if he sticks at it, even if some of his stuff can't be blown up past 15" now, some of it would be worth buying at that size.
Learning is another thing. Unfortunately for return-policies, I'd say it takes a few good months of practising before even thinking about calling a new body not suitable, even if you're already proficient with the software and have a workflow setup for another body already. I've been playing with Hugin for stitching panoramas lately, i've learnt so much in the last 2 months that i'm going back to the originals I made when I started and re-stitching them, they look so much better just from my skill increase (with the same program and same input files).
As for the OP comment about lenses. I'm one of those people who hate seeing CA and purple-fringing in high-contrast photos. But I just don't feel like spending the time learning how to de-CA them. I know which lenses are the culprits (my Zeiss Sonnar 180/2.8 for example, even worse with a 2x T/C), so instead of PPing, I just shoot accordingly, and avoid those scenes where the purple monster will appear. Someone else might do exactly the opposite, shoot everything and learn the software. Neither is right or wrong, but everyone has a preference.
More than that, I'd rather get a better lens. I did a direct sharpness comparison of my Samyang 35/1.4 to my 15-85. Never mind that it's a zoom, never mind that it has a 15-34 and 36-85 range added on, never mind that it's smaller, and has IS and very-nice AF, but I just haven't used the 15-85 much since. I hope I will when I travel again one day, or I may as well sell it.
I also hate cropping, because I can never decide what looks better. Or maybe because I compose with the viewfinder and it's already perfectly cropped. I don't just pull the trigger and hope to get somthing that looks better later. I'd rather take the scene as I see it out in the field or wherever, and only rarely crop, like when i'm already at 300mm.
And it's been said already, but just take the shot, and fix it later, better than no shot.