Celtx has released version 1.0 of their software and has added some new features. I've switched to Celtx a while ago and use it for my script writing. If you're buying software for Screenwriting and stuff, don't! Best part about Celtx is, it goes way beyond simply writing scripts. It's basically a pre-production kit. Check it out. Download it here.
Watch Mike's video about the new features. [thx Christian]