When it starts to get embarrassing!
My sewing room is in what used to be the living room, so it's the very first thing people see when they come over. I don't keep it looking like a showroom or anything, but I try to keep it looking at least like a productive space and not like a quilting store exploded in there. Right now it's getting towards the "exploded" look, I'm actually planning on spending some time in there cleaning up this weekend.
I'd love to get myself set up so that I could have a couple people over for a "sew date" and have space for them to set up their own machines. A couple ladies at work have been making noises about starting a sewing club so I want to have space so I can host sometimes!