I get this feedback when running YSlow on websites using your GREAT plugin:
The IE-proprietary AlphaImageLoader filter attempts to fix a problem with semi-transparent true color PNG files in IE versions less than Version 7. However, this filter blocks rendering and freezes the browser while the image is being downloaded. Additionally, it increases memory consumption. The problem is further multiplied because it is applied per element, not per image.
The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE. If you absolutely need AlphaImageLoader, use the underscore hack _filter as to not penalize your IE7+ users.
Wanted to pass this along in case there was a fix for this in an upgrade. Or is this not really of any great concern?
Thanks again for a FANTASTIC plugin.