Great article, it is rather photoshop centric though.
PNG is a really neat format to produce from code when you're trying to visualize datastructures as well, and some of these optimization tricks can be used with the GD library as well when you select the image type.
If you produce a lot of those images the bandwidth savings can be quite considerable.
They're good tips but unless you're addressing a large audience on 28k or less of bw then you're just as well to use pngcrush and be done as this will give you nearly all the optimisation with barely any time spent.
Just did a single test - 6MB file for an advert I did yesterday. 10K bigger with optiPNG than with pngcrush (using defaults) and took longer to process with optiPNG. I'm not bothered enough to test further ...
Also the optiPNG website doesn't say it's based on pngcrush, it does appear to have started by using the same methods though.
PNG is a really neat format to produce from code when you're trying to visualize datastructures as well, and some of these optimization tricks can be used with the GD library as well when you select the image type.
If you produce a lot of those images the bandwidth savings can be quite considerable.