I use them to carry a big U lock for my bike.
It is perfect for my netbook, but my full size laptop doesn't fit.
This is a really high quality bag. The three point system is particularly useful for situations where you are going to be moving quickly. If I pull the straps tight, I can do a cartwheel and barely feel it shift. Also, is it very water resistant. I have been using it for cycling, and none of my stuff got wet at all after a 30 minute ride in medium rain.
The bag is, however, very small. I tend to pack light, but if you are used to filling something lile a northface borealis, this bag will take some adjusting. It also poses a bit of a learning curve for your body, and it took my left shoulder about two weeks to fully acclimate. Overall, great bag for climbing, cycling, day hikes, and city use. I would reccomend it to any friend.