Reflections and Recommendations on Notebook Cases and Sleeves
This past Spring, I decided that I wanted to stop carrying so much "stuff" with me every day. 
Up to that point,
I had been using an STM Alley shoulder bag every day, and I really liked it.
It was just big enough for my MacBook and most of the accessories I needed a daily basis or when traveling. But when I thought about it, did I really need all of those things on a daily basis? Video adapters, remote controls, USB drives, etc. were all nice to have, but I rarely used them except when traveling or doing presentations.
After looking at several sleeves, I decided to give the InCase Neoprene Sleeve a try.
Although very basic, it provided excellent protection for my MacBook, and it was very lightweight. I could also squeeze a legal pad, very thin file, or magazine into the sleeve if necessary. After a few months, I found myself wishing that it had a little pocket or some way to carry smaller items, but it was certainly more than adequate for its intended purpose.
When I got my MacBook Air in June, I decided to look for a
new case. The InCase Sleeve would work fairly well, but it did not hug my new Air snugly enough for my taste since it was designed for the thicker MacBook.
Plus, I was still hoping to find something with that little pocket because I had gotten the Verizon 3G USB Modem, which I want to keep with me at all times.
After looking at all of the bags on the market at that time, I decided to give the Marware Sportfolio Sleeve a try. 
This sleeve hugs the Air like a glove, providing excellent protection, and it has an external "Orca-skin" pocket which can snugly hold an iPhone, USB modem, or other similarly sized items. The list price of this sleeve is less than $35, and I highly recommend it if you are looking for something that provides great protection along with a little bit of storage space.
Have you looked at any of the new TSA-approved cases that are supposedly easier to take through an airport? I love my InCase sleeve, but I'm also looking for a larger, travel-friendly bag.
I prefer a Brenthaven case for my MacBook Pro: foam pads the laptop on all four sides in the middle of the case, and there is plenty of room for files, cables, and everything else. The best briefcase I've ever owned. See http://www.mymac.com/showarticle.php?id=1999
I've had sleeves before and used them with a traditional briefcase, but I prefer my Brenthaven Pro 12/15 case for my MacBook Pro 15. The laptop is surrounded by foam in the middle of the case, and there is plenty of room for files, cables, and everything else. I've used it for over two years carrying it everywhere, and it looks and feels like new. The best briefcase I've ever had! See http://www.mymac.com/showarticle.php?id=1999
I used an STM Alley to tug around my trusty iBook/Macbook through 3 years of law school and it never let me down. Unfortunately, it's just not professional enough to take to court and it's too big to fit well into a briefcase. Still, the build quality and comfort were top notch. Highly recommended.
I went to the Marware website and found a bag for my iBook for $5.00.