How big is the Ripple network?
I would estimate that there are 30 public servers and 11 validators as I'm typing this answer.

I estimated the number of public servers by connecting to a number of servers and collecting the node keys of every server connected to them. While node keys are free to change, each server has a unique node key while it is connected. This is used to drop duplicate connections. So this should count each public server once.

I estimated the number of validators by collecting the validator public keys of every validation I saw published over a five minute period. I counted the number of unique validation keys.

I can't see any reason these counts could be too high, but they certainly could be missing some.