A question came up in today's class about the missing Variations adjustment option on some of the students' machines.
Here's the explanation from Adobe, "Note: The Variations command is unavailable for indexed-color images, 16-bit images, and 64-bit versions of Mac OS."
Also, Send Video Preview to Device and Video Preview are only available in 32-bit versions of Photoshop CS5.
Here's a note on the TWAIN issue some have reported: "TWAIN - The TWAIN scanner plug-in is no longer installed with Photoshop CS5, but is available via web download. Supported when running Photoshop CS5 on 32-bit Windows or 32-bit Mac OS. Also supported as a 64-bit application on 64-bit Mac OS with scanners that support 64-bit scanner drivers. The TWAIN scanner plug-in is also supported if you run Photoshop CS5 as a 32-bit application on 64-bit Windows or 64-bit Mac OS."
To run Photoshop CS5 on Mac OS as a 32-bit application:
Select the Adobe Photoshop CS5 application file, installed by default in the Applications/Adobe Photoshop CS5 folder.
Choose File > Get Info, and select Open in 32 Bit Mode.
Deselect this option to run Photoshop CS5 in 64-bit mode.