Feel free to copy/paste this entire post to other Firefly forums, but please credit http://www.JacquelinePassey.com/ and let people know they can go there for updates.
The official website for this information http://www.cantstopthesignal.com/ appears to be updating now.
Officially SOLD OUT: Atlanta, Austin, Boston, Chicago, Dallas, Denver, Hartford, Kansas City, Las Vegas, Minneapolis, Philadelphia, Phoenix, San Francisco, Seattle, Washington DC.
Tickets possibly still available:
Miami, FL http://tinyurl.com/77t32
Norfolk, VA http://tinyurl.com/czddo
Portland, OR http://tinyurl.com/8l6zr (Rumor has it there are problems purchasing tickets online -- you might want to check with the theater directly.)
Sacramento, CA http://tinyurl.com/a62vv
Does "sold out" really mean sold out? Some of the "possibly still available" cities are rumored to be "sold out". However there are other rumors that is just a software glitch, and if it is really sold out it will tell you as soon as you click on the screening time, not at the end of the purchasing process.
Tickets are already being resold on eBay: http://tinyurl.com/drgox