Save the screenshot to any number of places, including your computer or to Screencast (online free storage). Sharing to Screencast returns a convenient link which is copied to your clipboard. Paste the link in an email (instead of pasting an image). Your email recipient will thank you for not bogging down their inbox. The image stays in your online storage until you delete it.
You can also make a video recording of your screen actions by selecting the video icon instead of screen capture. You can record audio as you record the screen action. The resulting output is a SWF file which can be shared just like the screen capture.
Check it out: http://www.jingproject.com/
Mac and PC versions are available.