If you're curious what yard sharing is, "yard sharing is an arrangement between people to share skills and gardening resources; space, time, strength, tools or skills, in order to grow food as locally as possible, to make neighborhoods resilient, kids healthy and food much cheaper."
It's a great way to connect with friends, families or meet your neighbors. Think of it as a "Meetup.com" for gardening. You basically log on and create a profile at Hyperlocavore and find people in your area who are interested in either coming to garden on someone else's plot or offering theirs up to gardeners.
There's also a seed sharing section which encourages veteran gardeners to share seed with the less experienced.
Photos of SFGs in Austin and Lockhart, TX, via squarefootgardening.com.