No I posted about this. The overwhelming response I recevied was that for "most" things having separate Boxster and Cayman forums was duplicative, for example Boxster wheels and tires vs. Cayman wheels and tires. They are the same offsets, etc. so no real difference between the two.
Next we combed the Boxster forums to see what was duplicative and what was unique. The unique items were the Boxster Board discussion of Boxster items only, and the Boxster Pics and Videos. So those forums are only seen when you log into the BoxsterBoard.com site. Likewise the Cayman Discussion and Cayman Pics and Video are only seen when you log into the planet-9.com site.
The rest of the forums which were duplicative were merged and then shared across both forums, so on the Cayman site you see the forum "Cayman and Boxster Wheels and Tires", likewise on the Boxster site you see the same forum, a post in one shows up on both sites, etc. they are shared multi-site forums. (They do NOT show up on the Panamera site btw).
So now if you do a New Posts search on the planet-9.com site you will see all the Cayman specific items, plus all the shared Boxster items, plus the other shared Multi-Site forums (like off-topic, regional, rss feeds, etc.)
The BoxsterBoard.com site still allows those who log in there to get at Boxster specific content but also the share content coming from the planet-9.com site. This way we help keep the community together while still providing a means for having some unique items as well.
Hope that helps to explain it.