Cleaning down-filled items: Any luck?


So, I've been tossed up about a cleaning project and thought I'd get your input. I have a great featherbed that is in serious need of a cleaning. I've had it for about three years and every few months I'll vacuum it and Febreze it. I've even taken the chance and scrubbed it down with a cup of soapy water, but that only created gross looking watermarks. I'm sure that the easiest solution of all would just be to get a new one, but I'm determined to at least take a chance at giving it a good washing. I've done some digging around online to see if it is at all possible to machine wash it, but as expected there are mixed opinions. Plus, based on my experience with a down filled comforter, these items tend to get extremely heavy when wet.
So, what are your thoughts? How do you clean your down filled items?