I'm calling it The iTunes of Screencasting, not because it looks like iTunes or manages a library of your screencasts, but because it does the one thing that I love seeing applications do: it takes a process that formerly involved many small tools that worked together but were poorly integrated and pulls them into one coherent whole.
Kids today don't remember what we had to go through to listen to music on computers. First you had to rip the CD to AIFF files (being careful not to entirely fill your hard drive!), then use an encoder like Mpegger to convert them to MP3, then add the IDv3 tags in another app, then organise them in files in the Finder (I still can't believe that people still yearn to do this part), then use Audion to make playlists. Once you'd done all that, you had to go digging for those playlist files in the Finder, open them and play them. And you couldn't just Spotlight-search for them, or make a Smart Folder. Oh, no.
This is the kind of simplification that Screenflow delivers for screen and audio recording. You launch it, you choose your video sources (screen and/or iSight), you choose your audio sources and you hit the Big Red Button. You do your stuff, and then you tweak it afterwards.
"Tweak it afterwards" makes it sound lightweight. It's not. In other screen recording software, such as Snapz Pro X, you define a region of the screen to be recorded and if a dialog pops up somewhere you didn't expect, you start all over again. ScreenFlow does away with all that: you record the entire screen, and zoom in or crop the video later. That alone justifies the application for me. You can also add highlights such as cursor circles, click targets and sounds and keystroke overlays - all automatically and all after the fact.
Put that all together and it means this: focus on recording your demo, forget DJ'ing all your screencast software at the same time and edit with ease. Fantastic application.
[Update: Here's a link to a short video showing you how to sample a hung application: How To Sample An App (4MB Quicktime)]