I've been telling my clients (most of whom are accountants, insurance brokers and the like) to delay moving over to Vista until there's more widespread availability of certified drivers, until it's easier to get sufficiently beefy hardware at a sensible price, and until after Service Pack 1 has emerged to remove all the bugs it shipped with and replace them with new ones.
However the message didn't get through to my accountant's father, who has a new PC running Vista Extra Cheap Home Edition. The machine had been running fine for four or five weeks, and then started running v-e-r-y s-l-o-w-l-y for reasons he couldn't work out.
He'd installed Roxio This, Roxio That and Roxio The-Other, a collection of bits of software which allow him to do things with his DVD-writer drive. This includes Roxio Drag-to-disk, which on earlier versions of Windows allow you to drag files onto an icon so that they get written to the writeable CD... but which on Vista installs an unstable and uncertified not-really-a-driver, resulting in the PC taking two or three minutes every time you turn it on to decide whether or not it can load the "driver", and then failing. So I uninstalled the offending bit of software (and it's associated "driver"), and it works fine.
If you're going to run Vista, only run it in the configuration it had when it came out of the box. Or alternatively choose a more mature, stable and forgiving OS.
Or, even better, get me out to visit and give me money to uninstall the unsupported applications you installed yourself.