Distribution of nonces and hashes
Here we analyze the nonce values and hashes for all the valid blocks in the blockchain:[1]
Time Evolution
Nonces vs Hashes (y-axis logarithmic, x-axis linear)
This plot readily shows that the distribution of nonces that produce valid hashes is uniform.
Nonces vs Hashes (log-log scale)
In the animated version of this last plot,[2] you can really visualize the change in the difficulty and even see where the difficulty was decreased.
Histograms
Distribution of Nonces
The nonces found are skewed toward 0 because this is a selection effect: most everyone starts searching for nonces starting at 0:
Distribution of Hashes
Although the distribution of hashes is not uniform, this does not matter; all that matters is that the distribution of nonces is uniform (which they are, minus the selection effect of starting at 0):
2-D Distribution of Nonces & Hashes
2-D histogram of hashes and nonces (logarithmic color scale):
This also illustrates very well that the distribution of nonces is uniform.