Netcraft are an English Internet consultancy who have for years published a monthly survey of the server software on the ‘net. It’s quite interesting.

Apache held its own for a long time, but it’s down from its peak of nearly 70% in 2005. If you look carefully at those graphs you’ll see that the horizontal lines (ordinate lines?) aren’t spaced at 10% intervals, so be careful when trying to read values off the graph. My guess is that they are intentionally misleading.