This functionality has been long time requested by SolidWorks users like you, as a quick way to determine the smallest box you can package your model in.
Watch this video and tell the good news SolidWorks 2013 brings to your colleagues from the estimating and shipping departments.
They will love you for that!
Update: After I finished creating this video I realized that this new functionality will be priceless for users involved with 3D Printing by minimizing the support material and the printing times.
I am pretty sure you have spotted the same opportunity, but, just in case you are in doubt, I will try to prove this point next week with a second video on how to use the new bounding boxes enhancement for saving time and money while 3D Printing.