I still don't have any number about it, but I don't think small software companies can keep their patents a long time and still make profits with it. I don't see why a big company will pay royalties to a smaller one; Either they'll buy the patent, push them into a standard group (which force them to charge smaller royalties) or create another invention that do the same thing in another way around. Software patents have the flaw to be easy to circumvent (there is always more than one way to do anything in software). At the end, the only things that make patents profitable, is wide-spread adoption, which is usually a feature of only the biggest company or free software (which cannot held any royalty with patent) can afford.