You say it's simplistic and only took you a short amount of time, but even despite that it's obvious a lot of hard work went into it and it certainly shows!
I've stated numerous times that I"m not a huge fan of Vocaloids and that's simply because of the sheer quantity of work out there featuring Miku in it, but a scan like that begs to be walled, simply for the amount of artistic things you can do with it. Obviously I'll state the norm. Nicely done with the vector work and I'm glad you kept as much of the original image as possible, since it greatly aids with the background that you created. I especially love what you did with where her hair leaves off in the scan.
Now, to add on that, I love the abstract style you've gone with here. Generally speaking, I've found that the whole circle-stuff is becoming far too much of a common piece used, yet you keep it simple and make it incredibly fresh here. As previously mentioned, I love the little circles after her hair, sort of symbolizing the process her hair goes through after the scan stops. You did a wonderful job sticking with a color scheme that beautifully compliments the scan, yet doesn't drown it out with too much of it. Gotta love the variety in style and tone. I seriously love how simplistic this wallpaper is, and yet how it isn't by it's own right.
Overall, I think what I've said pretty much sums it all up. A cute, light-hearted wallpaper that flows perfectly and makes for an excellent treat on any desktop during the summer!