Finally got my first interlaced GIF spam! Here's the raw message: http://Puffin.net/software/spam/samples/0003_interlaced.eml and a page containing each frame extracted into its own separate GIF, followed by the "whole" raw GIF: http://Puffin.net/software/spam/samples/0003_interlaced.htm
Each frame was aligned at (0,0), filled the entire logical viewing area, and had no unusual GIF extensions. As I mentioned a month ago, I'm using a similar technique to ImageInfo, with the addition of pixel "density" and number of frames tests, so this spam was easily caught (by a little qmail filter running after SA). In a week or two, I should have some Area and other stats from a ham GIF corpus. Just sent the crunching software off to the volunteers a couple of days ago. - "Chip"