What a lovely and practical gift idea. What a great friend you are, Mac!
Hmmmm, there are so many gorgeous bags out now that I think I'd just like to add a practical slant to this discussion which may be of assistance if you narrow it down to two or three bags you like.
If you decide to buy one of the fold out diaper bags, make sure that the side pockets are all able to be zippered (or at least buttoned) shut.
It isn't a lot of fun as a new mum to be holding a screaming, wiggly baby complete with a dirty nappy and then watching in horror as the baby talcum powder and zinc cream goes flying out from a side pocket of the nappy bag right across the room, when the bag is opened in a flourish of desperate activity. (Oh, the memories....)
I'd also make sure that there are enough pockets AND that they are big enough to hold spare nappies, wipes, diaper bags, creams and a change of clothing. (Oh, and maybe even formula if baby is being bottle fed.)
I must add that a *washable* insert (that the baby lies on when changing a nappy) is also useful. I would also probably be inclined to go for either a patterned or a darker colour, just because lighter colours can show dirt and other mess a lot faster. Shiny fabrics are also something to watch out for - be sure to check how stain resistant they are. (Sorry for making babies sound like they are incredibly messy (and leaky!). They really are adorable! )