[Note: found this unpublished and unfinished draft of a blog entry I wrote early last year. Thought I'd publish it anyway.]
Like several of you, I've heard back from most of the schools I applied to (actually, all but1). I've had two in-person interviews (both followed Skype interviews), one just over-the-phone interview, and two acceptances (weirdly, not following interviews at all).
In-person interviews are the only way to go. I know SO much more about those schools, the city I would potentially live in, the faculty, grad students, and general climate of the program than I would have otherwise. In both cases they were game changers - I went in with set opinions that were totally blown out of the water. I literally don't know what to do with the two outright acceptances (without interviews) I did get. How am I supposed to make a decision based on the few pieces of paper they sent me? I'm planning to request visits.
In-person interviews are exhausting. Much more so than you think they'll be. I'm pretty sure I stopped forming coherent sentences about three-quarters of the way through. But it's okay, I think they expect this, and hopefully don't judge too harshly when you forget important pieces of information - like your name, where you're from, or who your POI is. And trust me, you get asked that a lot.
Similar-seeming schools and departments can be wildly different.