[Icer5k]

Interesting concept, especially with the recent changes Google has made to GMail/Apps. The biggest benefit/downside that jumps out at me is the complexity required to run an email system this way - Cassandra clusters, LDAP, external MTAs, and web severs all need to be managed. Obviously every email system requires these components to run, but most full-blown systems handle the relationships between components on their own.

TL;DR - Looks great for large businesses or maybe as a platform for a startup, but not as a hobbyist project.

[Down_n_Out]

I was thinking the exact same thing, I'd love to test it out, but for the moment (it might change in the future, I'm being hopeful) it's a tad too complex to setup for even a test ... I will keep an eye on the project though!