I've learned more about image opacity in browsers than I thought there even was to learn. Turns out that Internet Explorer has it's own alpha filter style tags for opacity, Mozilla invented a MozOpacity style before CSS added an official opacity style in CSS 3, and Safari, in version < 1.2, adopted Konqueror's custom KHTMLOpacity style. Oh, and Opera doesn't support image opacity in any way, shape or form (so much for supporting CSS3)! Neither does IE 5.2 for Mac OS X, but we already know my thoughts on that one...
As much as I hate to do it, Opera users are just going to miss out on a snazzy interactive feature of the new web site. The effects are way too cool to make the other 99% of the world miss out on them.
Maybe soon I'll post a preview of this effect. :)
The problem with IE is that it doesn't display correctly the alpha transparency by default whereas FireFox does. The alpha channel allows to create AWESOME effects for the PNG-transparent images, without losing colors.
If you use the GIF format, you can make transparent images, but they won't be more than 256 colors, and they won't look that nice... You can't make smooth edges or drop shadows... Now if u use the PNG format, you can keep all the effects of ur transparent images, and all the colors (16 millions) thanks to the alpha channel. This is the format to use if u want to create icons, but if u want to make a website using PNG-transparent images, it'll be awesome for sure, but some people won't view it the way it should appear (if they use a browser different from FireFox) !
It's really not about transparency in an image, it's about fading an image to be semi-translucent throughout.