com.me.photoshop_backup.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<!-- This file is stored in ~/Library/LaunchAgents -->
<!-- type in terminal: launchctl load ~/Library/LaunchAgents/com.me.photoshop_backup -->
<!-- Or you can log out and log in (launchagents are added automatically) -->
<dict>
	<key>Label</key>
	<string>com.me.corey.photoshop_backup</string>
	<key>LowPriorityIO</key>
	<true/>
	<key>ProgramArguments</key>
	<array>
		<string>osascript</string>
		<string>/Users/corey/Applications/photoshop_backup.scpt</string>
	</array>
	<key>StartInterval</key>
	<integer>600</integer>
</dict>
</plist>

photoshop_backup.scpt

if appIsRunning("Photoshop") then
	tell application "Adobe Photoshop CS3"
		try
			set theDocument to current document
		on error
			return
		end try
		if theDocument is modified then
			save the current document in file ("Macintosh HD:Users:corey:Documents:Photoshop:Backup:" & (name of theDocument)) as Photoshop format appending no extension with copying
		end if
	end tell
end if


on appIsRunning(appName)
	tell application "System Events"
		if exists process appName then
			true
		else
			false
		end if
	end tell
end appIsRunning