So while filing rates continue to be high (although as you see from the linked graph issue rates have been falling) the patent office has become better educated about what should be and what shouldn't be patentable (not perfect yet but its getting noticeably better, if only because patent examiners are entering the market who grew up in a digital age).
So a side effect is that when the patent claims for issued patents expire, that's it, no more revenue. You can perfectly legally implement the RSA key exchange algorithm now (as an example) without infringing on any patents. This was speculated to be the primary reason that RSA Data Security Inc was trying to get people signed up to use their Copyrighted implementation of same, since if you licensed the copyrighted code, and then decided to stop paying them license fees and implement it yourself they couldn't sue you for patent infringement but they would want to go through your code to see that you hadn't used large parts of their software in your new design. That approach was unavailable if you hadn't been given access to their source code.
So starting in 2010, and accelerating until 2020 all of those patents that were issued between 1990 and 2000 will revert to being public domain. It is one of the reasons I predict a tech boom in 2015 - 2025 :-).
I did not anticipate however that prior to their death that these companies would go all out in try to extract some, possibly any, value from them by suing the pants off everyone. I don't know, but I suspect that this is at least partly responsible for the current fracas.
[1] http://www.wolframalpha.com/input/?i=patents+us
[2] http://blogs.forbes.com/docket/2010/09/02/patent-marking-law...