I was just reading this piece on the “three layers” of the Cloud by David Linthicum — incidentally, David will be keynoting Gluecon. I think what David proposes is a useful framework (useful because it’s not overly nuanced) for thinking about the Cloud. Briefly:
Layer 1: The Basics of Infrastructure as characterized by storage, middleware services, communications, virtualization, compute services. Companies typically thought of as “IaaS” vendors are here (Rackspace, Joyent, Hosting.com, etc).
Layer 2: Utilizes the core infrastructure of Layer 1 to build out platform and management services, as characterized by companies like SFdC (force.com), NetSuite, RightNow, Windows Azure, enStratus, and a TON of other PaaS and SaaS companies.
Layer 3: Utilizes Layer 2 to build value-added services and components for the layer 2 offerings, and is characterized by the “app marketplace” phenomenon we’re seeing explode right now.
Within that framework, Glue is trying to take a look at the connective tissue that runs both horizontally in the layers and vertically between the layers. At Layer 2, for example, you’ll see security and interoperability standards, at Layer 3, things like activity streams, etc. Granted, we looking at a lot of stuff that isn’t strictly “connective,” but I think it’s fair to say that even in the event of things like Drizzle or the NoSQL stuff, we’re examining things that *enable* connective pieces. And it’s not just the horizontal connections that are useful, it’s the VERTICAL ones.
My thoughts around this aren’t fully formed, but really that’s why you throw events like Gluecon. 
As always, I hope you’ll come explore all of this with us.
