The new icon happened a while ago but not all computers it seems. My 10.5.7 still has the incandescent bulb icon
http://discussions.apple.com/thread.jspa?messageID=9483222
http://discussions.apple.com/thread.jspa?messageID=9483222
On the other discussion: All the hints I have point to a release of Mac OS X 10.6 _after_ WWDC, probably in early Autumn.