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

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/ http://dean.edwards.name/IE7/) didn't really catch on.