I'm considering a smaller bag - maybe a Imago or Ristretto for iPad - for my "I don't feel like carrying much weight or bulk" days. Days when I can get by with my 8.5x11" portfolio, an iPad, iPhone, headphones, wallet, checkbook, multi-tool, some pens and pencils, and a point-n-shoot camera. This bag would probably go on my Christmas Wish List.
I'm also considering a larger bag - leaning toward ID or Cadet - for my "I need it all" days; this one I would purchase for myself, since it's more expensive. It would be for days when I need to take my 15.4" MacBook Pro and/or a lot of files and notebooks in addition to all of the stuff listed above.
I'm good at selecting and buying items for other people, but I really dislike and am lousy at making purchasing decisions for myself. Especially when patronizing a site like yours, when there are so many wonderful products and many have features I can see being really useful.
If it's any help, I carry my (non-TB, highly stupid) backpack when I need my MBP, files, books, etc. and carry my MCB on days when I just need my (paper) notebook, iPad, lunch, and essentials. It's a good system for me, and really beats carrying my whole backpack when all I am bringing is my lunch and a pen.