During my MS Windows days, I made use of SnagIt!, a commercial screen grabbing application, to get ful images of a webpage I was browsing.  It did a wonderful job capturing even the longest of pages with it's auto-scroll feature.  Plus, I can specify which parts of the site I only like to capture.  But after recently moving back to Ubuntu, I no longer had access to the application.  I was suddenly left with the only option of using the "print screen" button several times and using GIMP to stitch them all back together or crop to the area I only needed.  The Ubuntu repositories didn't turn up anything even near the functionality provided by the MS Windows application.

Fortunately, a few minutes on Google provided me with an answer.  Abduction! is a Firefox add-on allows me to save a whole or even part of a webpage as a JPEG or PNG image file.  It actually provides the two features I only ever used with SnagIt!.  Install the Abduction! add-on in Firefox.  Go to the page you want to grab.  Save the file as an image (you can find it in the File menu or just simply right click on the page).  A new window should come up with the whole page selected by default.  Use your mouse to specify the particular area you only want to capture.  Choose if you want it in JPEG or PNG then choose to save it! 

This has definitely saved me a lot of time wasted from trying to stitch images back together. :)