If you'd like to read more about Mountain Lion, here's a few links to other interesting sites posting about today's surprise announcement. I'll add to this list as I come across more sites.
- Apple's own video trailer
- Download Messages beta
- Loopinsight.com's Jim Dalrymple's writeup
- The Verge has a writeup and a video preview
- Macworld Hands on with OS X Mountain Lion
- Macworld Hands on with Gatekeeper
- Macworld Hands on with Notification Center
- Macworld Hands on with Notes and Reminders
- Macworld More on Messages and iChat
- Macworld has a podcast with Jason Snell and Christopher Breen talking about Mountain Lion.