Last Friday Chris Hernandez, a Microsoft Software Engineer, posted benchmark result data to show how Microsoft had managed to get the Windows 7 upgrade time to be faster than, or at least equal within the five percent, to the Vista SP1 upgrade time. One data point however stands out in this sea of numbers, and that's the one that shows how upgrading from Vista to Windows 7 (32-bit) where the system has 650Gb of data and 40 applications could take as long as 1215 minutes on mid-range hardware.
Note: In case you're wondering, 1215 minutes works out at around 20 hours, 15 minutes.
Now, from a plain PR point of view, releasing these numbers seems crazy, after all, people are going to latch onto that 20 hour figure and run with it. After all, it's a pretty big number, but it's a number that has to be taken in context.
First, Hernandez has been open and published data for the Vista SP1 to Vista SP1 upgrade (more commonly used as a way to repair a system), and for similar hardware and data/application levels, the same upgrade takes 1306 minutes, fully 91 minutes longer.
Secondly, a data load of 650GB stored within user profiles, along with 40 applications installed is a lot of data. In fact, 650GB of files, 40 applications, plus Windows all crammed onto a single 1TB doesn't leave much breathing room for an upgrade.
Finally, unless you're a total data litter bug and cram your user profiles with videos, I can't see many reaching this data level. Those that do handle a lot of data keep it separate to their Windows profile, such as on a separate partition, or better still, drive.
That said, I'm not letting Microsoft off the hook that easily. One of the issues that I feel needs addressing in Windows is how Microsoft encourages users to store data on their Windows drive/partition when there are other drives/partitions available. Windows doesn't do enough to encourage the user to store files on separate drives, and external drives. In fact, it's all too easy for inexperienced users to fill their desktop with files.
I've carried out a few Vista SP1 to Windows 7 upgrades on a few mid-range systems that I class as "in use" and home to both a modest amount of data and applications and these systems were upgraded in under two hours. It would have to be a very cluttered, very full system for the upgrade to take nearly a day!
Ideally though, it's best to do a clean install and copy your data back across and then reinstall your applications. That way you get the best possible upgrade, and the least hassles. It seems like more hassle initially, but in the long run it's worth it!