Question:
I’m used to the Photoshop crop tool which is awesome. In Photoshop you can enter the final size you want to the cropped image to be, You then select an area of the original image and Photoshop maintains the correct aspect ratio while you drag. You can then adjust the crop area to get it perfect. And when you accept the crop then final image is re-sized automatically to the settings you entered. Like I said awesome! So I was wondering if gimp worked in the same way.
Answer:
Nope.
The hard way: Use crop tool. 
- Check fixed.
- Pick “size” from the drop-down.
- Type in the width x height.
- Click somewhere on the image.
- Change the fixed drop-down to “aspect ratio” (text box will reset to “current”.)
- Drag the corners of the crop area to perfect your selection.
- Click inside the crop area or hit enter and the image will be cropped.
- Image>Scale image and in the dialog adjust the size.
The Easy Way: Use the selection tool. 
- Check fixed.
- Pick “Aspect Ratio” in Drop-Down.
- Type Desired Width : Height (use colon not x).
- Make Selection on image.
- Image>Scale Image and adjust size.
Answer Links:
http://docs.gimp.org/en/gimp-tool-crop.html
http://www.youtube.com/watch?v=2rGGpOTSpbc