One feature I sorely miss when using linux is the snipping tool, which makes taking a snapshot of a piece of your desktop a breeze.
By default, there's no equivalent to this tool built-in by default and there's no real dedicated application available that does this either. There is a neat little trick that replicates this function and you may already have most of the software installed on your Ubuntu machine.
Using Ubuntu Software Center (or synaptic package manager) make sure you have these packages installed related to Compiz. What these do if you don't already know is enable some special effects for your desktop.
You can also go ahead and install "Kolourpaint", which is a cool MSPaint clone for linux.
Now go to:
System->Preferences->CompizConfig Settings Manager
In the left panel click "Extras" and in the right panel click the word "Screenshot".
Under "Use This Plugin" check off "Enable Screenshot" and under "Launch Application" type "Kolourpaint". That's it, you can close the window now.
To use it, all you have to do it press and hold the window key while you drag a box around what you want to capture. The image will be automatically saved to your desktop, and Kolourpaint will open it up immediately. If you don't want Kolourpaint to open then just omit it from the steps above. Enjoy!