While it wasn't my intention to continue along the shadow theme, here I am anyway. Something I've noticed is that when I look at a scene with shadows, I'm not always cognizant of the contrast shadows cause. Like many scenarios in life, our brain adjusts certain things our eyes see.
When I saw my cat sitting in the window with her catnip squirrel, I was only vaguely aware of the shadow. It wasn't until I took the shot and looked at it on the screen that I realized how much it darkened the top portion of my cat.
So what do you do when you have a strong shadow like that? You could set your exposure for the darker portion, but in this particular shot, it would blow out the lighter areas. I did try a layer mask to balance it out a little more, but it actually looked worse. For the image below, I added an adjustment layer in which I lightened up the entire picture, bringing some of the detail back in the dark portion (although the lower area is rather pale).
Another option would be shooting in RAW and making adjustments in your post processing. Because I haven't used RAW (yet), I can't tell you more than this. I could also have raised the shades to remove the shadow altogether.
The other issue with this particular shot is that the shadow formed a very distinct line that will never be entirely eliminated. Just another reason to pay attention to the lighting and make the right choices before you take the shot. The more aware you are, the better photos you'll create.