Customized and derived distributions

It would be fun to see a graph of distributions in which edges showed "derived from"
relationship and size of nodes showed approximate number of users.  Should be doable with
graphviz!

I know that approximate number of users is a hard number to measure.  Maybe just have a few
sizes of nodes depending on base-10 order of magnitude: 10,000 users, 100,000 users, 1,000,000
users.  Are there any Linux distributions that have one million users?  Not very many.  Are
there are any Linux distributions that have 10,000,000 users?