Presently I am using Final Cut AV (Mac version). It's a great piece of software for what it was designed to do - offer a simple, clean and elegant writing platform for AV production. Unfortunately I and, I suspect, a good many others were left high and dry when the makers announced that they would no longer be supporting the product with version upgrades that will work on future Mac operating systems (Lion, etc.).
Looking for an alternative, I was delighted to discover Celtx, which can format in the same simple "two column" format. I was disappointed, however, when I discovered that it was a "two step" process. One must first write in one format (text editor) then convert it to another. Not the most elegant solution.
I would like to see the AV mode improved to emulate the feature set of FC AV, including the ability to write and edit directly in the two column format, automatically line up dialog and video, create scene breaks, etc.
FC AV was one of the best pieces of scripting software, specifically for A/V production, on the market. Would love to see Celtx fill in that vacuum with an AV mode that matches FC AV, feature for feature.