I've been around animals for almost all my life and it always amazes me how perfectly "designed" they are. When an animal is living in the most natural best way possible they are healthy and happy and a joy to be around.
Once criticism that chickens get are that they are dirty. By which I assume people mean stinky and/or they get poo on on them. I will attest that the birds themselves are not smelly. They do have strong smelling waste but that is typical of most birds due to the fact that they don't urinate. Our birds have a pretty big enclosure and we rake it every day to keep it from building up, so this is not really and issue. Plus, we only have 3 birds total.
As for the birds feathers, they can get a build up on their bottoms but only when they aren't roosting properly. When we first brought the 3 birds home, we created roost spots for them by repurposing and hanging horse buckets filled with hay. We also put hay in the corner of the coop. And they did get their feathers a bit messy at times because they were sitting down. But then we built a sturdy roost pole for them (which they love) and now they stay clean and mess free.
It's important to make sure they stay clean and dry. A build up of waste is not healthy or attractive. Not only could they get infected but they could also become egg-bound, which is fatal.
Now that they have a proper option for roosting and sleeping, our hens are lovely and clean. With cute fluffy butts!
See cute chicken butts on Flickr.