I agree with the timing if not the sentiment.
Ds's room was pretty much a store room for the first 6 months of his life. He never even went in it because he was in with us. It just contained cardboard boxes full of baby stuff.
We put the cot together at 6 months old and did a bit of "decorating" then. Just putting up posters, a mobile, one of those soothing light projector thingys- to make it a bit more comfy and interesting for him.
He's 2 now and has a bed, wardrobe, trofast storage system, comfy chair, plastic boxes full of toys- its a proper bedroom.
On the walls he has stickers, posters and pictures cut from calendars and magazines. He has primary coloured paper balls (left over from Christmas) hanging from the ceiling and funny little trinkets hanging in the window. The projector and mobile have been put away for the next kid.
Its all been put in place bit by bit as he's needed it and all been chosen with him in mind. So, for example, there's loads of pictures of elephants because he was really into them at one point.
I personally would not decorate a bedroom for an unborn child. They don't really need their own space for some time and by the time they do, they can help you pick stuff out.