Shutter is a billed as a feature-rich screenshot program, which it is. But I'm just taking my screenshots with the Print Screen key. What I'm after is a quick way to add annotations (arrows, blurs, circles, etc.) to the resulting images. Under Windows I use Irfanview for this and it works great.
But Shutter is MUCH better at this task than Irfanview and I'll tell you why:
The editing tools produce vector-based graphics and they 'float' above your image until you save it. This is really a nice feature, since in the bitmap-based Irfanview, once you've made the edit you're pretty much done, unless you use the undo button.
With Shutter you can move your edits around to position them or resize them before saving, and there is no clutter to the tools, just the features you need right at your fingertips.
Here is the editing view of Shutter:
|Shutter's edit view with the tools at left.|