It’s impossible to tell anything from this story about the effectiveness of exercising an Exit Option. It should be expected, anyway, that the option itself does the work, even if pulling the trigger has to contribute to the general credibility of virtual exodus.
As an exemplary case, however, it would be hard to beat. From the statement by Preston Byrne, of eris:
If [the Communications Data Bill] is passed into law, we are likely to see a mass exodus of tech companies and financial services firms alike from the United Kingdom. We are happy to lead the charge. […] In keeping with our promise in January to leave the country if the Conservatives were returned to power with this policy on their legislative agenda, we have promptly ordered all of our staff to depart from the United Kingdom and to conduct all future development work abroad. […] Additionally, with immediate effect, we have moved our corporate headquarters to New York City, where open-source cryptography is firmly established as protected speech pursuant to the First Amendment to the Constitution of the United States, until such time as we can be certain that the relevant provisions of the Communications Data Bill will be stricken from it (otherwise, we will reincorporate in America and continue our business here).
(To add a “Go eris” at this point could be reasonably criticized for redundancy.)