Really, you can do this with Jing, which is more feature rich and also easier to use. http://www.jingproject.com
It's Java, so it might work on Linux, I dunno. I haven't tried. I don't have the Java plugin installed, and don't consider it worth bothering with at the moment. But, if it did work on Linux, that'd be enough for me to use it occasionally. Big projects would still make me reboot into Windows to use Camtasia, but it would definitely take the place of Jing (since I wouldn't have to reboot).
For Twitter buzz, throw some stupid badge in there that says, "works with Twitter!"
Jing looks like some kind of Tonka Truck toy. Design matters, Screenr has that down. Now for revenue... not sure, I just know that Twitter wins big time w/ the way Screenr is setup.
The finished video isn't very good at displaying text, so it is really hard to read.