Despite a slow debut among the enthusiast and developer communities, Vista x64 is now making some serious headway, according to a post on the official Windows Vista Team Blog:

We've been tracking the change by looking at the percentage of 64-bit PCs connecting to Windows Update, and have seen a dramatic increase in recent months. The installed base of 64-bit Windows Vista PCs, as a percentage of all Windows Vista systems, has more than tripled in the U.S. in the last three months, while worldwide adoption has more than doubled during the same period. Another view shows that 20% of new Windows Vista PCs in the U.S. connecting to Windows Update in June were 64-bit PCs, up from just 3% in March. Put more simply, usage of 64-bit Windows Vista is growing much more rapidly than 32-bit. Based on current trends, this growth will accelerate as the retail channel shifts to supplying a rapidly increasing assortment of 64-bit desktops and laptops.

64-bit PCs running 64-bit editions of Windows Vista typically have 4GB of memory or more. Compared to 32-bit systems, which top out at around 3GB of memory, 64-bit PCs can offer added responsiveness when running a lot of applications at the same time and have the potential for greater performance and new experiences as next-generations applications are written to take advantage of this new platform. What started out as a gradual (some would say "glacial") movement toward 64-bit PCs, driven primarily by technology enthusiasts, seems to have turned into a swift transition, likely fueled by the falling cost of memory and consumers' desire to get the most out of their PCs.