I would think that a distance function applied to random points with a Poisson distribution for your desired radius followed by a few tweaks like thresholding, exponent, uniform noise, and erosion would generate a result fairly close to this. The Poisson distributed point set (a jittered grid is a simple to compute approximation) gives you the centers of cells that are roughly the same size, the distance function gives you a smooth distance between points with nice cellular boundaries between blobs, the threshold ensures the cellular boundaries become clear, the exponent to make the blobs a little less linear, noise and erosion to add the fine-scale stochastic element. I'll see what I can do this evening about synthesizing this sort of thing.

Any spectral sythesis fractal generator that has a cellular basis function should be able to give similar results, especially if the cellular result can be applied only to the first octave or so (think crocodile skin or cracked mud shaders).