I guess there are people here who feel that their photographic talents are being constrained by anything other than a full-frame camera and they are trying to justify the cost of upgrading to a full-frame. Well, why do you need justification from others? It's really a simple matter: if you have the budget, then you should go ahead and get one.
Don't talk rot about FF having more "pop" than APS-C. There are umpteen number of photos (and photogs) out there shooting APS-C professionally and their photos have equal amount of pop as anyone else shooting FF.
Don't believe me? Here are some samples from Flickr (these aren't mine, but they illustrate the point - and they were shot with a Rebel T2i):
http://www.flickr.com/photos/robbyryke/6846645823/#
http://www.flickr.com/photos/ilovelotsofpizza/4675165898/#
And if these still do not have enough pop and don't jump out of the screen/print, then maybe ya'll should consider this camera: http://www.shopfujifilm.com/detail/FUJ+16082969
I guess it has something to do with what you shoot also. From my perspective, I shoot a lot of my images at larger than f2,0 apertures, and that gives the FF cameras a huge advantage, but other styles may not be THAT much different, for example at f11 snapshots with useless light

But these two examples, to me at least, prove the difference I see with my own images. It's too snapshotty.
This is my personal taste, and I'm not here to dog the aps-c, but for ME, the images will always be better no matter what you shoot with a fullframe. And extremely often, isn't very difficult to see what image shot with what, although there can be a garabage picture with a FF and a fantastic, optimal with an aps-c camera that won't tell the whole story. But there is a reason Canon released the FF cameras, and we will see more of them.
The x-factor or magic of the FF camera isn't that at all. It's much smoother gradients between light and dark, less depth which really show off the smoother better bokeh of those lenses used, it's better dynamic range and less noise.
My last comment for this thread, I just had to argue with that it's "no difference, it's all light and skill and framing" it isn't.....
it's the same as saying it's better to buy a polarizer than a better lens, no it isn't, because they also sell polarizer for the more expensive lens. It's the same as saying, learn how to sharpen and shoot raw and you don't need the more expensive lens, but you can also sharpen the images from the more expensive lens , so the better gear will always keep their advantage....