[ChuckMcM]

   > I love the separation of concerns that is possible with ... one team working on the API and one on the interface

That is, in my opinion, the larger point. If you can do solid 'interface driven design' then you enable rapid evolution on both sides of the API. One of the things Jon Wall and I did at NetApp was prototype a better split of system across the RAID and Filesystem layers, that split achieved 50% better performance across the same spindles and it allowed for innovation in the file system layer that was currently hindered by "all the hooks into the RAID stuff".

The key though is picking the right layering, and not having too many. Like hashes in perl you can go crazy and suddenly everything is an API and simple things go through n layers and bog down.

When people tell me they want to be architects I ask them questions about layering, that is where you separate the good systems thinkers from the not so good ones.