I commute to work by bike nearly every day - the only exceptions are when I need a complete rest day for training or an upcoming race, or if it's actively raining in the morning. I also incorporate commuting into my training plan. So I'm pretty specific about what I need out of my commuting back pack.
I previously used the Timbuk2 Classic Messenger Bag (review here) and had a few basic complaints: during out of the saddle efforts it moved around way too much, and during heavy downpours rain sometimes gets in on the sides of the opening. Otherwise it was a pretty good bag - I like how it looked, the materials were hardy and sweat/rain proof, and it was a good value. I decided on the OGIO All Elements Pack Stealth because racing season is coming and I'll likely need to start doing some out of the saddle efforts again during my commute, and really would like to do them without worrying about my bag (It was also on sale at the shop, and I love a deal).
SPECS: $129.99 / 2.5lbs / 1600 cubic inches storage / completely waterproof with a roll down closure system / Airflow back panel / Laptop and tablet sleeves / hip and strap belts
I've been using this bag for about a month, and I'm happy with it. The material is pretty heavy duty, and there is ample space for my clothing. I have not stopped by the grocery store with it yet, but believe it could hold enough groceries for a dinner or two, and a bottle or two of wine in addition to my clothing.
How securely it is attached was the main reason I wanted the bag, and I've been pleased with it. There is a ridge for airflow down the center of the bag, and that helps to keep the bag seated along my backbone. The shoulder straps are grippy, and the the cross straps attaching the shoulder straps together is secure. The waist strap anchors the bottom of the bag, which is crucial during hard out of the saddle efforts. The bag also sits high on my back, so it doesn't interfere with my core-lower back-glutes movements during efforts.
The only complaint I have about the bag is it's not very visible (I know, I know, "Stealth" is in the name). I understand that this is also not a bag specifically for commuting by bicycle, so being loudly visible is not a priority for safety. I'm planning to attach reflective strips to the bag to make it more visible.
PROS: Snug, secure attachment, enough space for everything I need for commuting, durable.
CONS: Not very visible, a little pricey.
RECOMMEND? For someone commuting and using their commute for training like I do, I would recommend this bag. For someone commuting more casually or who commutes/rides in their work clothes, it may be a little more performance than is needed for the price tag.