NPR: When Patents Attack!

I write software for a living, and I have a hard time recognizing redeeming value of software patents (other than to have something to negotiate with when someone tries to sue a company). Reading the NPR transcript about patents got my blood boiling. The system has been gamed, and patent troll companies legally extort money from other companies.

Read or listen here. Are there good reasons to have software patents, and if so, on what types of inventions and in what circumstances?