On: Ask Hacker News: What is the most undervalued web technology? (2me RSS)

If it's just undervalued tech, and not "what's the most powerful tech that's obscure" I'd say it's the PNG file format. Lossless, greater color-depth, and alpha-blending: PNG would make the most difference on the most number of average people's web pages if they used it. Some of this other stuff is a lot more powerful, but it doesn't get my vote for undervalued because I think the audience is anybody who is creating a web page, not just tech guys.

I'd say there are really only two reasons that have stopped widespread adoption of PNG:

1. The file sizes can be rather large (less of a problem these days)

2. IE6 improperly displays PNG alpha (This is big one).

Even the "IE7" javascript hack (http://dean.edwards.name/IE7/) didn't really catch on.