Hey Effrem,
I use the Tumi case...as I carry a lot of documents with me... The case a a protective casing to protect from damage. I used to have teh 15inch PB, and when I switched to the 17inch I did not notice a considerable weight gain..
Here's the link to the Tumi model that I have...
http://www.tumi.com/products/index.c...3_Link=Details
If you are in the market for cases, there's a great Macnn thread that contains virtually every case makers for the apple:
http://forums.macnn.com/showthread.p...hreadid=178702
Hope this helps