Now that I've added a 3rd "controller" hub an installed @srwhite's excellent HubConnect I am trying to figure out a good strategy for how the apps will be distributed etc...
The general idea with using multiple hubs has been to increase stability by distributing the processing to separate hubs while strengthening the communications to the devices themselves.
In terms of basic layout there have been different ideas - some prefer to separate via device & protocol (Z-Wave hub + Zigbee hub) in order to minimize interference and strengthen the networks respective meshes. Seems easier to troubleshoot specific device issues.
Others have split things by "area of effect" - having a hub in two or more locations supporting both Z-Wave & Zigbee devices. The idea is to provide as strong a signal to devices as possible reducing hops.
In addition some have opted to add a 3rd (or 4th!) "controller" style hub which does not connect to physical devices but is used instead to hold all the custom apps / cloud services. The idea being dedicating a hub for this reduces processing issues even further by isolating possibly slow or cumbersome apps that could adversely affect device communication and event handling.
In my case I have 3 hubs - An upstairs hub which controls (ZW+/ZB) devices, a main floor hub that controls my basement and main floor (ZW/Zw+/ZB) devices and a 3rd hub which I was using for development but have decided to also include as a "controller" hub.
When I had 2 hubs - I used HE's "hub link" and tried to keep things as simple as possible by only exposing a couple of virtual switches. I did this because I was still not sure about how things would work.
Moving to 3 hubs got me thinking about what to put on the controller hub vs the client hubs. I have a bunch of different devices a lock, thermostats, leak detectors etc. Some rules like motion activated lighting I feel should stay on each hub with the devices they control for optimal speed/reaction + reduce error potential. Others like APIXU weather app or the Nest app seem good candidates for the controller hub.
Be curious about others thoughts on this..