When we looked at what was out there, we found nothing quite fit.
A backpack means sweaty backs, high center of gravity, and your laptop taking a beating while riding. (Backpacks are designed to hold laptops with flat backs, not curved like when you're riding your bike. Ouch.)
Messengers solve some problems, but they're uncomfortable on the body, especially when riding. They tend to move position, making it distracting and annoying (always falling to the side).
Panniers are popular with some bike commuters. They're great for carrying large loads but are overkill when you just want to bring the essentials.