I'm on 1/10 acre as well, in Portland, and find that having defined boundaries (fences and curbs) makes intensive, stacked designs easier to manage than when we had 10 acres. Keyhole beds and guilds can pack a lot of food, habitat, and biomass generation into a very small space. At first I worried that I wouldn't be able to pack all my favorite fruit
trees into such a small yard, but once I got to know some of my neighbors, realized that their yards are my orchard and vice versa--one fruit tree produces far too much for one or two people. I just planted what was missing from my neighborhood.
Gaia's Garden was written for people with 1/4 acre or less, so most of what's in it applies to small yards. And a key concepts in
permaculture are stacking, layering, and small-scale, intensive systems. So, if I do say so myself, it's applicable to urban lots.