A couple of minutes ago, I entered my first Jira issue for Second Life: VWR-1591. It's a new feature request concerning the snapshot feature in the SL viewer, which lacks some features imho.
I've been using the IBM Lotus Sametime 7.5.1 instant messaging client's screen capture tool, which is great. It allows you to capture a part of your screen, annotate it or draw a freehand line on it, and then paste it in your chat automatically. The SL snapshot feature is much less sophisticated, it only allows you to capture the entire screen, and you can't edit the result before sending it off as a postcard.
So, please, have a look at issue VWR-1591, and vote on it if you're so inclined. There's also a couple of screenshots attached there, that show how the Sametime 7.5.1 screen capture tool works.