First up, this really jumped out at me when i saw it. It's a fairly passive, yet still intricate background, with a single image in the middle. Very effective.
The vector: yes, it is amazing. I love the way you've flared the wingtips gold and kind of left the rest to fade into the background. The colouring seems a little out-of-keeping in the centre, however (basically where her left foreleg is) - I, personally, think it would have worked better to simply have a straight gradient from the wingtips to the legs. The mane and tail are a nice contrast to the outlines of the body, although the tail seems to muddy up with the background hexagons. The cutie mark is just fantastic.
The background: The gradient is fantastic - pink to black with some gold near the bottom. The hexagons are transparent enough that they don't steal the image, although I think it would have been more effective to put them behind Fluttershy, rather than in front of her. I'm not sure what to think of the little gold flare in the corner, although it seems to work fine here, and adds a nice little flourish. Overall, the background matches very well with the central image. Well done!
Overall - 4 and a half stars. This is a marvelous wallpaper, and is sitting on my desktop as I write.