vellum is great with scrapbooking--it has a nice look. It works great as on overlay--you can see the object behind but it is kind of muted--In my books I have placed vellum over a picture and journaled on the vellum.
Also when my youngest son was born--for the thank you cards--I had copies of black and white photos made--used vellum, in baby blue, as the overlay to cover the entire picture and that was the front of the card. They were very cute.