I've given this some thought. I'd like to see how Sencha put together their massive CSS files. Which tools were used and what methodologies were followed. I'm not terribly interested in specific cross-browser techniques or Sencha Cmd although both are relevant. I'm interested in how you tackled and organized such a task and what patterns you followed in the creation of the style sheets. I would imagine that intermediate knowledge of CSS would be required to attend.
I think your expertise in this area would definitely help your customers craft an approach towards the development of their web apps. It's not necessarily Sencha product specific but it would be invaluable.