Windows 7 Upgrade Could Take Over 20 Hours
The upgrade to Windows 7 could take all day and night, literally.
While we're not going to dispute that a clean install is the way to run Windows 7, there are going to be many users who will choose the literal upgrade path from Windows Vista and perform an in-place upgrade.
The reasons to do an in-place upgrade are numerous. First of all, the core software changes to go from Vista to 7 aren't as drastic as previous generations of Windows. Secondly, the convenience afforded by the in-place upgrade allows users to retain nearly all software and settings without the need to restore any previously backed up data.
Another possible advantage to doing an in-place upgrade is time – it's supposed to be faster than starting fresh and reloading all your old programs. But in some cases, the upgrade could be the more time-consuming route.
Microsoft's Chris Hernandez of the Windows Deployment team detailed Windows 7 upgrade performance as compared to Vista SP1's upgrade behavior. Hernandez found that Windows 7's upgrade speed was faster than Windows Vista. Interestingly, the time it took for Windows 7 to upgrade from Windows Vista SP1 outpaced that of a Vista SP1 to Vista SP1 upgrade procedure.
At its very worst the upgrade from Windows Vista to 7 was found to take a whopping 20 hours. At that rate, a user would likely have less downtime if he or she just did a clean install and restored/reinstalled programs.
Most users will average upgrade times lasting just a few hours, but those with slower systems or exceptional amounts of data will have to set aside a good portion of the day just for the automated process. All clean install systems upgraded in around 40 minutes or less.

Sure upgrade install.
Upgrade with all the viruses/spyware/malware/trojan w/e that's on your old system your virus program didn't detect.
So you used statistical outliers to make an intriguing headline for an article of little to no relevance for any of the readers of this website?
Thank you for wasting my time.
Think of it as retraining. MS is increasing your value to your employer.
I said nothing about fresh installs. I referencing the information about UPGRADES, specifically "Most users will average upgrade times lasting just a few hours"
Meaning that, of the set of users who wish to take the UPGRADE rout, MOST of them will have acceptable install times.
It's like creating a headline along the lines of 'Residents in southern California can experience more than 2 strokes per year!".
It is not an invalid statement-there is in fact a very small percentage of that population that do, but its abusing statistical outliers to make an otherwise nonexistent newsworthy story.
*cough* snow job *cough*
I backed up 200 gigs of goodies and did a fresh install in a few hours, most of the time was just transfering data to old slow drives. =D
I did an upgrade to Win 7 on my machine and it took about 3 hours. A full install of Vista took about an hour(not including installing drivers) so I think the 20 hours is an extreme case not the norm.
Upgrading from Vista is a better option for me because all the drivers are installed. Clean install is better but not faster.