When you select a 3d object and press spacebar or enter, it deletes it. I'm not sure of the functionality of this, but it seems like asking for trouble.
I've deleted things countless times and pressed Ctrl+Z, but new users won't necessarily notice that they deleted a bunch of things, especially since most commands include pressing enter and if you press enter once too many it will delete the thing you are working on.
Again, I'm not sure why you would not just press "delete" instead of assigning delete to some of the most used buttons that have nothing to do with delete. Seems like a UX oversight.