I've been using Snow Leopard for five years now, which is getting on to Windows XP longevity. Having left academia, I just now figured that whatever was keeping me on that tired platform has probably gone to the grave, and moreover Mavericks looks a lot more enticing than Lion ever did. Ergo upgrade.
So far no real problems, apart from new (empty) windows in Chrome interacting in a nasty way with Spaces. I lost my RSS feeds, as I knew I would; there's a widget in Chrome that is somewhat usable but a long way from either Google Reader or the old Mail.app. Conversely the new Mail.app seems a bit faster and less buggy... though it keeps hitting up IMAP servers from a lifetime back. I had to reinstall MacPorts, as always. clang seems a lot faster than GCC. My venerable perl blog script broke, as always. Fast times.