Don't miss this excellent article in The New York Times by Claudia A. Deutsch, "For Love and a Little Money." It discusses the growing trend among retired volunteers to ask for a paycheck -- even if it's only a small one.
This sentence says it all: "Many retirees have learned, to their irritation, that what they give free is discounted as fluff." Meanwhile, one semi-volunteer (who negotiated a largely symbolic salary) is quoted as saying, "An organization and a person are simply more committed to each other when the person is paid."
This makes perfect sense, and reminds me of the discussion that the nonprofit world had several years back about whether to charge fees to clients. Many organizations found that by charging even a small fee, clients were more likely to show up for appointments and to appreciate the services given.
Of course, the article raises the specter that all volunteers will want to be paid. However, I doubt this will be a big problem. The people profiled were long-term volunteers, putting in many hours per week. Your average volunteer just can't, and wouldn't want to, sign up for such a major obligation.
In fact, many organizations have the greatest success at attracting volunteers by offering short, even one-time opportunities to do meaningful work. The unpaid volunteers who sign up for these keep their freedom, and can change their mind (or even flake out and not show up) every once in awhile.
But the article does raise an interesting possibility for nonprofits who've wanted to open up a new staff position, but haven't been able to come up with enough money, or even hours of work, to make it worth hiring someone. This might be the time look for a retired professional who will work for a stipend or a token salary. (Just don't use this as an excuse to shortchange skilled workers.)
For more on how to manage your nonprofit's workforce, volunteer or not, read Starting & Running a Nonprofit: A Practical Guide, by Peri H. Pakroo (Nolo).