Before using Greenshot I used the Windows 7 provided tool called SnippingTool.
What is missing in Greenshot and very useful in SnippingTool is the ability to have a thin frame around the screenshot.
This is useful when you capture some white background region and want to delimit the capture region when copying it in a word document for example.
You can do this (in ver 1.2) with the Border menu entry from the Effects icon. It doesn’t give you any control over line color or line thickness. It’s always black, but you can apply this effect multiple times to increase thickness as much as you want.