According to a report given by NASA to Congress in late May, NASA is prepared to allow other government agencies, and even private corporations, use of the U. S. lab section of the ISS once the station is completed, which is scheduled for 2010. That has always been the plan, so it's good NASA is thinking about how it will proceed.
Experimenting on ISS may be frustrating for corporate users, however. Let's suppose a major pharmaceutical firm does research on ISS and finds a compound that works against all cancers, to pick a disease. If that compound can only be produced in microgravity, we will all be in a kind of limbo. ISS has no production capability. We would be in the position of knowing what would save Aunt Jane's life, and unable to give it to her. Building an orbiting pharma factory to produce the stuff, and developing infrastructure to get the product from space to Earth would take years. In the case of cancer, governments around the world would presumably cooperate to try to speed the process, but for less infamous diseases, or nonmedical products, the translation from lab to store shelf might be painfully slow.
That is, unless the plans of a few entrepreneurs work out. There is a handful of small companies working on developing ships that will reach Earth orbit regularly, safely, and comparatively cheaply. Many of them are headed by people who have already proven they know how to make money-- Sir Richard Branson, Elon Musk, Jeff Bezos. Another small company, Bigelow Aerospace, is working to perfect inflatable structures to be used in space. The first test structure is in orbit now; a second is scheduled to be launched shortly. Bigelow plans to have a man-rated habitat ready to fly before 2015. Such a huge structure could have many uses-- including, no doubt, housing a microgravity drug production facility that could be serviced by ships flown by another private company. By the time NASA is ready to open the American lab on ISS to others, it might have competitors with even bigger ideas.