While I’m on the topic of useful software for RPGS (though more for RPG bloggers than GMs and players), I find Scribefire really useful. It’s a Firefox plugin that lets you quickly highlight something on a web page or blog post and write and publish a blog post to your own blog quoting it. I used to use Diigo for that, but it’s too many extra steps. (Diigo is a web service that lets you highlight and annotate other people’s web-pages in a way that persists for you when you return to them, and it’s really quite neat as a research tool–but overkill for just posting in response to something you just read, and you have to delete a bunch of the boilerplate it inserts every time.)
There’s a bunch of other functionality in Scribefire (like when you are actually looking at your blog’s homepage it gives you a toolbar to quickly write posts, upload images, etc.) that I haven’t really explored, but for the basic function of swooping a highlight on somebody’s post, composing a reply and publishing it I couldn’t be more satisfied.