I had a 350D, when I upgraded to a 40D I really liked the improvement in ergonomics. However, as a wildlife shooter I was looking for better AF, better high ISO and better cropability (= more quality megapixels).
When the 7D arrived it seemed to tick all the boxes. I was quite nervous buying it given some of the critical comments on the forums re: AF and ISO. Anyway, I took a risk and got the camera. It took me 3 months or so to convince myself that this is a significant improvement on the 40D.
When you have good light, I've really noticed the difference in terms of detail capture. The 7D excels here. When the light is bad, if you set the 7D to a +0.33 exposure setting you will get some great low light images (way better than anything I got with my 40D). Some images I have at 3200 ISO are incredible compared to what my 40D would have produced!
Ultimately, how do you judge a camera? Let me tell you one way, are you getting better images with your new camera than you did with your old? For me, my 7D is a leap ahead of the 40D. Highly recommended.