I actually like registries for weddings but I never buy anything off them for baby showers. There are things that a new mom and dad will always need, no matter how many they already have, like diapers or onesies. I think it's a pretty easy task to shop for things for a baby, such as clothes and other things. In fact, sitting in the back seat of my car is a baby gift I am shipping off that doesn't include a single thing off the couple's registry, but are all things that are fun and useful. I also like to give unique, fun things that they wouldn't otherwise receive.
For a wedding, I do find it helpful to know what a bride and groom wants or needs to start their new life together. Really, you only need one toaster, blender, etc. I don't want to duplicate any of these items. Although, off topic, I'm not sure a lot of people know how to read a registry anyway. Looking at my friend's registry, several people kept buying things that were already "fulfilled" and so they received 4 clocks and 5 mirrors.