I use a Yuba for errands about half of the year (this being Minnesota) with a 3 year old and now with a 1 year old. v3 with a (no longer produced) Peanut Shell seat, a Yepp Maxi seat, a couple panniers, and hopefully soon some Nitto Albatross bars swapped in to help with an upright posture for my back.
What kind of hills are we talking? I do okay in St. Paul/Minneapolis by carefully picking certain routes to avoid the worst of river valleys, but there' s a big difference between that and San Francisco.
Aside from that, I love it. Sure, it's a little heavy, but it mostly feels like a kinda heavy mountain bike in terms of handling. And I like knowing that I'll probably run out of space to actually mount cargo safely before I hit the maximum recommended load. It's a little slow getting it up to speed, but once I've got some momentum going even an out of shape rider with back problems can manage to comfortably go quite a ways. My grocery runs are about 5 miles roundtrip and I've often found myself tacking on a couple extra miles of joyriding at the end even with full panniers and a toddler.
See if you can find a bike shop in your area that stocks them, take one for a spin and see what you think. I don't know if I would get one without a local shop to help me since they've been very helpful in getting an arrangement of child seats and panniers working. It's probably doable on your own, but I'm not great with mechanical jobs.
