Photoshop seems to have an annoying bug (or feature) where it stops importing the clipboard. I often copy and paste screenshots from Firefox and Quicktime, only to find photoshop ignoring the new content. I thought it only applied to my old Photoshop 7, but it appears it affects all versions including CS3. This registry change fixes the issue.
Open the Registry Editor and add the following:
[HKEY_CURRENT_USER\Software\Adobe\Photoshop\10.0]
“AlwaysImportClipboard”=dword:00000001
Where 10.0 is your photoshop version.