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...