Tom Heyman Pieter Moors, and Gert Storms have published "On the Cost of Knowledge: Evaluating the Boycott against Elsevier" in Frontiers in Research Metrics and Analytics.
Here's an excerpt:
To get an idea about the success rate of the "won't publish" resolution, we checked signatories' publication history after they signed the petition. Using ResearchGate, Google Scholar, Academia.edu, LinkedIn, ScienceDirect, and lab or personal websites, we were able to compile a bibliography for a large sample of "won't publish" signatories. Due to the time-consuming nature of this research, we limited ourselves to two subject areas, Chemistry and Psychology, each with approximately 500 signatories.