There are _slight_ artifacts on the defocused green die. At typical Wikipedia in-article display sizes (400x300, in this case), this is acceptable. Viewing in Win Firefox 13.01, Windows gamma. I'd use tinypng on large files before downscaling for web use.
If you have a good downscaling tool it will create a larger number of intermediate colors when you downscale and you'll actually end up with a larger image!
