Windows Vista delivered some outstanding icons. The new icons in Vista are natively 256 pixel by 256 pixel images. This is great from an aesthetics point of view.
But there are some downsides.
First, any icon (whether in a program or elsewhere) that doesn't have a 256x256 version gets its 48x48 version used even if a higher resolution icon is available (such as 128x128 icons). This means that many of the great icon packages of all time that supported the 128x128 Windows XP icon format won't look great under Windows Vista.
Secondly, as you can imagine 256x256 is pretty big. To put it in perspective, the icon in this news item is only 128x128. A 256x256 image is FOUR TIMES bigger. So you're talking about a lot of artwork needed to make it look good (a lot more detail needed). This vastly increases the artistic capability necessary to make them.
The article linked below talks about some of the challenges. What do you think is going to happen?
