hi there. i have the moypak for my 12" powerbook and i really do like it. i too was concerned about size - as a fairly small person, i didn't want something overwhelmingly large or too bulky to carry around. the moypak is perfect for me and what i need out of a laptop bag - it's got just enough room for cables, my mouse, and ipod, and a rear slot pocket for a couple of folders and/or magazine. i wouldn't recommend this case if you needed to carry lots of books or paperwork with you - it doesn't have enough room for all of that.
with my pb and all above-noted accessories, the case is pretty light. the strap is well-padded, so it's not tough on your shoulder. i like the color and style of it since it's pretty low-key and doesn't even really look like a laptop case (a bonus if you're worried about theft or something). it's got just the right amount of small pockets/slots for business cards, pens, and disks as well.
so, overall, a great case in my opinion. i've seen a lot of comments here on the crumpler bags and others that offer lots of other features and color choices, so i think those would be worth looking into as well. but the moyapak covers all the basics, so i'd recommend that if it meets all of your carrying needs.
hope that helps! happy case hunting!
marianne