After nearly a year of waiting, that master Vista fix known as Service Pack 1 has been released to manufacturing, meaning it will make it to you sometime this month, perhaps on that February 15 date that had been bandied about.
This means better stability, faster file handling and improved device compatibility. It also contains some future proofing, including support for DirectX 10.1, UEFI firmware and ExFAT flash-memory file format. On the subject of overall speed, some early Battlemodo action suggests that there's a nice bump here.
In terms of reliability, Microsoft tells us, "SP1 users likely to have fewer disruptions," defining a disruption as anything from a full-on system crash to the likelier application failure. Microsoft quantifies this with "average time between disruptions." Initially on Vista, you could go about 17 hours without a disruption, now it's double that at 34 hours between disruptions. When I asked about how this compared with XP, Microsoft said it was a tough comparison, since they lacked the detailed telemetry on XP. (Perhaps this is a convenient shortcoming.)
As you might have heard, Microsoft is also claiming that, security wise, Vista is not only better than XP but that it's better than Linux and Mac OSX as well, using security updates to 10.4 Tiger in the first year as a comparative example. [Microsoft]