If there are icons on your desktop, you'll see that darker desktop background images that are fairly constant in contrast/brightness work best for trying to read (and scan over) icon text. This is why Tiger's background works so well, as did previous OS X releases - fairly constant darkish colour with only slight variations in an abstract way.
The grass background in previous Leopard builds was OK - but nowhere near as clear for reading text labels on icons as the Tiger background. Further, the water droplets look a little like the little blue lights in the new dock, adding further confusion. And finally, I think a default desktop should be something abstract rather than a seemingly random real life photo (what does wet grass have to do with anything?).
Now, if there really is a space background, it is interesting to see how this works. The one shown in that flikr account, as a background, works better that the green grass in terms of reading text on icons - though being so black means that the black shadows on text no longer show up on icons. The stars are going to look a lot like the little blue lights in the new dock once again though. I would say a space scene is a little more abstract than a close up of wet grass - I'd still prefer a more abstract background though. And a space theme is a little dorky - sort of like saying "hey, this OS is space-age!".