It's kind of a micro blog. People only have 140 characters to put in any one post so it's mostly what they're doing at that exact time. Since a lot of folks twitter from there phones, there's pictures of whatever they're doing.
I've noticed for the industry here, there's a lot of pictures being thrown around, updates to sites/blogs, appearances, and talk about their work. Aside from "I'm eating a salad," it's kind of interesting to see the industry girls as normal human beings.
http://twitter.com/FreeOnes_Petra
I have a good 100 porn stars and models on there, that really are them. ;-)