For everyone out there saying "I don't know anyone who uses these apps," keep in mind that a lot of iWork users are longtime Apple users, and some of us remember the bad old days where there was enormous hostility to any docs not in MS format.
I'm an author and I collaborate all the time. I use Pages daily (extensively), Numbers almost-daily, and Keynote about once a month. I've been using iWork for more than a decade.
But when I send someone a word processing document, I convert it to Word or PDF first, because non iWork users EXPECT all documents to be in MS format. So they don't know I write in Pages.
If I give a presentation, no one knows I'm using Keynote, because unlike PC users, I don't start my presentation at the Windows desktop; I start it with my title screen slide.
I collaborate with most people using MS or Google formats, but all the content is created in iWork. And every now and then I find someone who I know is using Pages, and then I stop having to convert things.