There are a few screen captioning software on the net for both Mac OS and Windows, I was in touch with IShowU in my Mac previously, but due to the incompatible it is with my Mac (Crashed everytime I start recording and I fed up to re-install), I go for Jing. With the easy captioning that similar to IShowU, now I don’t need to type when my friends ask me about computer setting 
Jing is a freeware screen captioning application for both Windows and Mac operating system.
There are only 3 options when Jing a running, for Mac OS, it will appear at top right corner as default, while for Windows, it will appear at middle top of the screen. Not only Jing will record your screen in flash format, it can directly upload to the net or flickr or better, a place where they’ll give free space for you to upload, not only all the internet and uploading stuff, Jing allow you to save the file in any place your preferred.
Jing has a very simple interface, from the appearance to the area selecting…
Of course, not only screen video captioning, Jing allow a simple screenshot as well. If pressing Command+Shift+3 or Print Screen keys are hard for you 
Still I’m not into captioning or closing a video I recorded on scene. Although I’m using Adobe After Effect as my video editing (iMovie doesn’t work too well on editing though), but After Effect just don’t work properly in Intel-based Mac though 
Good site screen captioning.
mediamovers: Yeap, much much more easier to use than IShowU