I recently wrote a paper for the February Cutter IT Journal called Runtime Collaboration and Dynamic Modeling in BPM: Allowing the Business to Shape Its Own Processes on the Fly. It’s available on the web to Cutter subscribers, and in the printed journal.
In the article, I deal purely with the topic of runtime collaboration, not collaboration during process modeling: how users participating in a process can add new participants for the purposes of collaborating on a step in a structured process, or even create their own subprocess at that step. I look at why you would want to do that (mostly auditability of processes) and how the results of that can be rolled back into process design rather than just being changes to a single process instance.
Disclosure: my payment for writing this paper was a year’s subscription to the journal, plus bragging rights.