The Fade In application log file, generated while it is running, can be found at:

Windows:
C:\Documents and Settings\<UserName>\Application Data\Fade In (XP and earlier); or
C:\Users\<UserName>\AppData\Roaming\Fade In (Vista/Windows 7 and later)

Mac OS X:
/Users/<UserName>/Library/Application Support/Fade In; or
/Users/<UserName>/Library/Containers/com.generalcoffee.fadein/Data/Library/Application Support/Fade In (Mac App Store version)

Linux:
~/.fadein