Elance is a site where you can find freelance projects through a bidding system. There are currently several different projects for medical or scientific writers, including ghostwriting for books, reviewing documents for medical accuracy, and marketing some health products. Using sites like Elance (and others) may not be a bad way to start doing some little non-clinical projects here and there. I wouldn't suggest that you rely entirely on these types of bidding websites if you plan to build a freelance career out of medical writing. Bidding can be so unpredictable.
More people are finding ways to build an entire career out of freelance projects. I like to get involved in some small things once in a while, but I don't think I could ever live the life of a full-time freelancer. However, I think it can be very beneficial if you gain some freelancing experience as an independent contractor, especially given the current economic state. If you can show that you have some freelancing experience, then you're likely to successful finding those opportunities in the future.