The global meshnet project

We have a real world network called Hyperboria (http://hyperboria.net) with various services (irc, video, social). Latency depends on the amount of peers you have and how well connected they are.

In addition to what abkco said:

The total latency between two nodes is not much more than the latency between every link along the route added up.

This means for a physical network, latency isn't bad as long as the individual links are good.

For Hyperboria, latency can be high at times because nodes are not always linked to other nodes geographically close to one another, so the packets have to jump around a little.