During Apple's Tuesday keynote address at Seybold Seminars San Francisco, CEO Steve Jobs (originally scheduled to attend the now-cancelled Apple Expo in Paris) announced that Mac OS X 10.1 will be on sale from this Saturday.

"Now is the time to upgrade," Jobs told the crowd of publishing professionals. "This is the mainstream release."

"We are halfway through the transition," he added.

The 10.1 upgrade will be available free of charge to all Mac OS X users through to October 31. It will be available on CD-ROM from Apple resellers. UK customers will be able to order the upgrade from Apple for about a £15 shipping fee. There will not be a downloadable version.

Apple VP Phil Schiller and various other senior product managers demonstrated Mac OS X 10.1 (and OS X Server 10.1), iDVD 2, AppleScript Studio, and Microsoft's Office v.X (due November).

Apple also announced that more than 1,400 applications are now available for Mac OS X 10.1.

More to follow...