I've noticed that higher res skins say 256x256 look terrible at lower resolutions than 4:3 1600x1200 or 16:10 1680x1050.
this could be easely fixed by making the Ui code recognize the images files in a skin folder and use prescaled bitmaps instead of scaling it with a fast and shitty looking algorithm

this is the maximum horizontal/vertical resolution that stuff looks good at depending on resolution

64px - 800x600/800x480
128px - 1024x768/1024x600 - 1280x1024/1280x800 - 1440x1080/1440x900
256px - 1600x1200/1680x1050 1920x1440/1920x1200

[edit] definitely not a priority but i just wanted to let people know.

or you could release version of the skin for each resolution

but that's a ridiculous amount of work, especially keeping all those organized.

Make the highest res, then run a down-scaling script?

Actually is there a problem with using higher res pictures for lower resolutions?
ie 256px with 800x600

yes it looks like someone ate shit and puked it on my screen...

the problem is screen ratio not resolution... you would need to do a high res in each screen ratio and then scale it to the resolution. The alternative is to do the screen oversize and chop it to the desired size for everyone.

Use SVGs instead of bitmaps where possible, then pre-render.