Its emphasis on getting screen captures and screencasts shot and shared makes the freemium application Jing extremely quick and easy to use for Mac and Windows users. I use its big brother, the professional capture app Snagit, at work (we take a lot of screenshots in these parts,) but I've often installed Jing on laptops and on other peoples' computers when I need something light and free.
The one irony for Windows users is that if you don't have the .NET framework installed, it adds a few more minutes of set-up time and a heftier footprint. The benefit is that you won't have to do much--Jing's installer takes care of the framework and of launching Jing after round one of the installation. This video takes on the Windows perspective for installation and use, but the program's main components will remain the same for Mac.
While Jing saves video clips and stills to your desktop, sharing is its specialty. Take your pick of publishing via Screencast.com, an FTP site, Flickr, or even YouTube, if you subscribe to the premium version for $15 a year. Upgrading also gets you access to recording from the Webcam, a neat feature you can use to narrate or introduce a screen recording.