It seems like CubePoints is a popular plugin, and Phil mentioned future integrations with WPMU Dev products. Here is how I foresee one of the integrations -- with Affiliates:
WPMU would offer a free add-on "module" to CubePoints that we could activate to allow incoming unique links, signups, and paid memberships to translate to different points levels.
This would be great! I was planning to give out points for *sharing* content across a multisite network. But it is much better to reward *results*! Bring traffic to the main site, or any site across the network, and earn CubePoints.
See my other post about connecting Affiliates with Floating Social too: