Nothing new, but more of a reitteration based on my findings which have mainly been w/ the brick textures.
Image resolution does help but it seems to be on a decreasing scale. So rendering small images will make the affect horrible. If you do images about the size of your monitor it'll be quite a bit better. But after you get past about 2000 pixels in either width or height it doesn't seem to make as much difference.
The biggest difference comes from changing the scale. Make the scale as large as you can without making it so big it's obvious the scale is way off. This is also a much better option for animations since you don't want to just try and solve the problem by making ginormous image files.
I haven't really tested it much but it seems logical that you'd want to use .png or tiff files since they aren't compressed like a jpg.
I usually combine all of these things. Scale the texture up, have SU render a bunch of png files at 29.97 fps at a nice big size (twice the size I'll end up with is pretty ideal), then use Adobe Premiere Elements 4.0 to put them into an animation.
-Brodie