Graham, I expect the driver situation to be much better with Vista x64. The 64-bit version of XP release was a weird, out-of-band release that never had proper levels of support. XP was released in 2001, and x64 XP was released in, what, 2005? That’s weird.
But with Vista, x64 is a first-class citizen, released at the same time alongside all its x86 brethren.
Of course it’ll still take time. Some companies still don’t have plain old x86 drivers for Vista that are any good. But within the next 2 years, I expect x64 driver support to at rough parity with x86.