I spent a number of years as the core of the R&D department of a small software firm. When copyright was the only available protection for software (in the U.S.A, that is), our management chose to hold everything as trade secrets. This essentially barred employees from disclosing our inventions to anyone outside the firm. Throughout this period we published almost nothing. We also grew quite cynical about seeing papers at PLDI (and other conferences) that explained innovations we'd made 3-7 years earlier. Of course, as trade secrets they remained unpublished until someone academic had the same idea and got a publication for it.
Then software patents arrived, and the whole game changed. All of a sudden we could ask our management "Is this a big enough deal to file for a patent?" If yes, we'd file -- thus disclosing the idea to the world. If no, we'd immediately suggest that we should publish. That way, no one else would be able to patent the idea out from under us.* We suddenly began publishing quite a bit -- all stuff that would previously have been kept secret.
My experience is that software patents led to an increase in disclosure of inventions.
* Yes, I know. The patent office really s*cks at finding prior art. Nevertheless, our lawyers told us that if we routinely submitted things for publication we'd be in a much stronger position if someone else got the patent.