The Wall Street Journal has a good article (subscription required) about companies re-hiring their retirees to cope with tight labor markets. These companies often use the retirees for part-time or temporary positions. The article featured Schneider the "transportation and logistics" company (which I would have called a trucking company), but the Immigration and Naturalization Service recently announced plans to bring back retirees to help clear the agency's backlog (reported by the AP).
I've posted before on the importance of bringing older workers into the workforce, (such as here). I think it will take some experimentation to get work the bugs out of a retire hiring program. Your retirees are likely to want more flexibility than when they were regular employees. A big part of why they will return to work is to feel that they are doing something useful, so make sure to express your appreciation. It will probably help if you facilitate social networking among your retirees. Some retirees find that they are cut off from their old social connections; work can help them.
We're still a few years away from the real labor crunch, but it's coming. The businesses that thrive in the next decade will be those that are experimenting now.