I'm also looking for a more practical similar sized bag for day trips hiking etc. I like the LowePro Slingshot, but I'm left handed, so they are not 100% perfect.
I can highly recommend the Tamrac Adventure 7 backpack. It's comfortable, it's got a slim profile, and it's discreet (at least in the gray/black version). The top section is big enough for a sweatshirt, lunch, and a novel. The bottom section can fit an SLR with medium-sized lens (e.g. 17-55/2.8 IS), + two more lenses (or one more lens + flash or tabletop tripod).
Richard, I picked up the Domke and am very happy with it as a day bag around town. Thanks.