Not too many average users on Twitter from my experience. I've maxed out the local people that I follow and it's mostly automated news feeds (managed by tech folks) and other tech people in my field and related who are Tweeting.

Sure we can all pull out a story here or there of someone 'average' discovering and using Twitter, but I'm afraid my experience on the whole doesn't indicate that your Mom or mine will be using Twitter anytime soon.

Facebook? Now that's a whole different story.