Hoodoo,
I plan on using it as everything from an overnight backpack, to a carry-on bag, or piece of luggage, to a gear bag.
I heard one other complaint like yours that said it seemed too big for a daypack, yet not large enough--or built like--a larger hiking pack. The thing of it is, however, the 2900 has something of an internal frame in it, like the larger packs.
I also like the idea of the larger capacity for the bulkier, lighter material, like you said, which makes it a very good overnight pack when carrying a foam mattress or whatever.