From LonghornBlogs.com:

Tom's Hardware Guide talks with ATI's vice president of their software divsision Ben Bar-Haim about "Vista-Ready" Drivers and discusses their stability.

Vista graphics drivers are programmed for a new driver model currently named LDDM (Longhorn Display Driver Model), although the "Longhorn" part is subject to change. According to Bar-Haim, the "user mode-based" drivers depart from Windows XP's "kernel mode-based" model, and are thus unable to crash the operating system: "Microsoft had concerns about the stability of drivers in XP when they noticed an unreasonable high amount of XP crashes due to device drivers. With LDDM, we can run the driver engine for months without crashing," he said.

This is definately another plus on Microsoft's part for Windows Vista. I'd like to install drivers without crashes. I want to be able to install an incorrect driver and have it just tell me that the device driver won't work with the specified device instead of possibly crashing the entire operating system. The drivers ATI has released for Windows Vista Beta 1 have proven strong and reliable as I tested Beta 1. I have yet to load the ATI drivers in Build 5219 as of yet.