Almost a year ago, Bjoern Negelman shared an excellent model for classifying Enterprise 2.0 use cases, building on ideas from Larry Hawes and Lee Bryant. I find it very usable when discussing the purpose of Enterprise 2.0 and different use cases. Below is a variation of his model that I use (with credit to Bjoern) when helping customers to identify Enterprise 2.0 use cases. You can download Bjoern's models from his account at Flickr.
[update: I've split the model into three versions]