Explosion of design
With the recent mention that IE7 will have proper alpha-PNG support, I predict that we will see an explosion of creativity in web site designs.
I've been pondering this in some of the recent design work that I've seen come out of the company that I work for. Imagine changing an entire colour scheme of a site without having to change a single image; even ones with feathered edges.
On one of these projects, I had a navigation button layered over a photo and a background. Instead of having to export the navigation for each photo, I used a PNG for the photo and for the button. The button appeared over the photo which appeared over the background. For each subsequent photo, I only had to export the photo. In the end, this saved me time and will save the user bandwidth.
Marko over at Maratz.com makes great use of PNG's at the top and bottom of the page (unless you use the current version of IE). It is effects like these that web designers will see as a real possibility for the masses and I'm sure will inspire a new generation of designs.