However, there's a problem with the wholesale replacement of GIFs with PNGs. First of all, PNGs don't support animation, so any animation information gets lost in the translation. A more significant problem is that major browser support for PNGs is still spotty, despite the fact that PNG has been a stable standard for years. Support for PNGs appeared in Netscape Navigator only in version 4.04, and in Internet Explorer in version 4.0b1. I have yet to find a version of Navigator or IE that supports transparency, let alone the more advanced PNG features.
Transparent backgrounds appear white.
Even the most current version of IE is mystifyingly incapable of displaying stand-alone PNG files. Because of these limitations, a site that jettisons its GIFs in favor of PNG risks breaking graphics for a significant number of users. Nevertheless, in the wake of the recent Unisys actions, many sites have begun to do so. No doubt this will put pressure on users to upgrade their browsers, and on browser vendors to upgrade their products' PNG capabilities. As a pervasive Web standard, GIF's days are numbered, killed by the greed of its owner.