The greens at Metropolitan Golf Links will be aerated August 29 and 30. Director of Golf Steve Porter tells me that Metro punches its greens with small tines and does a good job of filling all the little holes with sand, so the greens are quite playable after two or three days. Steve says you'll barely be able to tell the greens were aerated after one week.
Why do golf courses aerate greens? It's about getting air, water, and nutrients to the roots, according to the Golf Course Superintendents Association of America.
About.com features an article on what the rules of golf say about aerated greens (don't expect relief).