David Wallace, a leading young philosopher of physics at Oxford University, writes:

A random thought on the topic of “boycotting Synthese”. A boycott, to me, sounds like a decision not to use some product or service so as to send a signal, independent of the usefulness of that product or service to the signaller. I’m not sure if I’d want to boycott Synthese or not, but in a sense it doesn’t matter, because the current position of the EiCs means that I don’t feel confident that Synthese is a sensible place for me to publish, and so I don’t intend to send work to them; similarly, I’m not confident of the rules under which any referee report of mine would be treated, so I don’t intend to referee for them. I suspect quite a few people may be in the same position: ambivalent about officially “boycotting” Synthese, but not in fact planning to continue any involvement with it until the EiCs clearly signal a change of policy.

ADDENDUM:  Mohan Matthen (University of Toronto) writes:

David Wallace has struck a note very similar to my own feeling about a Synthese boycott. An organized and official boycott would suggest that Synthese is a valuable commodity that one is prepared to forego, at some cost to oneself, in order to force some action. Given what has happened, the value of Synthese has fallen. Accordingly, my motivation to submit to or referee for Synthese has weakened. But I wouldn't refuse to read something just because it's in Synthese and I wouldn't urge my library to cancel its subscription (though there are consumer reasons for action on the subscription front). And frankly, I no longer care very much whether the editors apologize or not. At this point, it wouldn't rehabilitate them or the journal in my eyes if they did–I wouldn't become more motivated to submit or referee.