Vista SP2 I hope?
It's impossible to say Jim because it would depend on the size of the drive it's scanning and the number of files and whether or not they had previously been scanned (the latest version omits files previously scanned unless they've been modified). It also depends on your McAfee SecurityCenter settings - whether or not scanning is using minimal resources (click pic below to enlarge if necessary). If that is unchecked it will run at full speed but PC performance may then suffer if you are busy with other applications. That also depends on the machine's resources, CPU speed and installed memory (RAM) size.
Why are you asking, is it taking an interminable time? If so you might want to turn off Scheduled Scanning and use the Custom scan option which has more parameters you can check/uncheck and just do it from time to time. I've found over the years that there is no need to scan at all unless the machine starts misbehaving.
By the way I moved this to VirusScan.
Well the scan has been running for 12 hours now and is only 22% complete. Does that seem unusual?
Very unsual. I think maybe you should conatct Technical Support Online Chat and have them troubleshoot.
All I know is when that happens it's often due to either corrupt files (Registry Cleaners often to blame) or zipped files that are double-zipped, such as on a hard drive that has been compacted.
The scanner than takes forever to unpack the files.
As peter says it also can be large multi Gb avi files that slows things up. The 2011 version can exclude thise in the custom and scheduled scan features once you scan them the 1st time.
Also if you auto upgraded from 2010 to 2011 version the auto update might have been corrupted so maybe consider an uninstallation and reinstall from your account.
The 2011 version scanning is 100% faster than the 20110 version at leat that is my view and the developers so something is slowing it.
How do I upgrade from the 2010 to 2011 version?
It should happen automatically eventually but as Tony has just said, it's possible it's corrupted so best uninstall and then reinstall from the account as per that link he gave.