I recently got a question about why we didn’t include the PNG “fix” for IE6 in Stacks.  It turned out to be a really good way to explain how we’re moving away from IE6 support in general, but moving away very slowly.

For those that don’t know what the PNG fix is, here’s the quick explaination.  Since Internet Explorer 6 doesn’t support transparency in 24-bit PNG images, we use a script that pre-processes the images through a special Windows filter and then replaces each PNG as the page loads.  Some of my products (like Blocks and Collage) do have the PNG fix applied to their images, but Stacks does not.

The simple answer is that a lot of themes now include the fix and a lot of people want us to to disable the PNG fix in our other products, usually to be compatible with a theme, and sometimes for other reasons as well.  In Stacks we’ve kept things very simple and totally script-free so that there will not be any chance of incompatibility.
The longer answer is that we’re taking the first steps toward making IE6 obsolete.  We have to support IE6, but the IE6 market share is now small enough that we have to look closely at the cost/benefit ratio of supporting IE6 at the detriment of the experience in other browsers.
For YourHead, these steps have to be very small.  We cannot afford to stop supporting a browser until it’s market share drops well below 1%.  So we’ll continue to ensure that all the features that we do offer, are features that work on IE6, too.  And that is the case with Stacks.
But as a first step we’ve decided to stop adding things specifically for IE6 that would tend to diminish or limit the experience on other browsers.  In our view the PNG fix falls into this category.  It’s useful for some things, but when used as an overarching methodology it impacts how many and what sort of PNG images you can use, it impacts how you can apply background images in CSS, and tends to conflict with other scripts.
In the future we’ll probably take bigger steps, like excluding IE specific CSS.  But for now, this one small step is probably far enough.
If you feel you need the PNG fix for some portion of a page I would recommend adding it by hand to overcome the specific image — or adding it to your theme (or choosing a theme with it built in) if you do feel you need it on a whole page.
Here’s a link to the original and probably the most widely used PNG fix around:  http://www.twinhelix.com/css/iepngfix/