In one way it is and in another it isn't.
The 50D is one of the camera's I have and to be honest the least pleasing and to be real honest I like my good old 20D more then the 50D but that doesn't make it a bad body.
You have to do some reading to understand I am afraid.
Start here(diffraction): http://www.luminous-landscape.com/tu...tanding-series/u-diffraction.shtml
The 50D diffraction kicks in around F/7.1(maybe even wider).
Many spotters like to use a Canon 100-400 for example which has a sweet spot somewhere around F/8 - F/11
and already the problem becomes visible, the 100-400 isn't good enough to make the 50D shine.
A diffraction calculator can be found here: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
As said this doesn't make it a bad camera but it is a camera with limitations.
If I know in advance that I am going to need big prints I"ll happily use it but only with glass of F/4 and faster.
And if you can live with these limitations and are prepared to invest in expensive glass you will have a cracker of a camera.
It might be worth to wait for the 60D though as it has been rumored to have extra computing power to combat diffraction.
Something I expect to be present in most next gen camera's because a resolution limit has been reached with the 15mP APS/c sensors and because diffraction is not some sort of magic fixed number like the speed of sound.
There are ways to fight it, even USM
works to some extend albeit at the cost of extra noise.
So I am kinda curious to what Canon comes up with.