Starting with Snow Leopard, it's no longer possible to message an application from within the context of another. Therefore, the AppleScript would need to be rewritten as

tell application "Remote Buddy" 
-- Reserve the fade engine for 5 seconds 
visualize effect "fadeReserve" for duration 5.0

-- Fade out to black in 0.5 seconds 
visualize effect "fadeOut" for duration 0.5 with color "black" 
end tell

-- Hide something from the user's eye, thus "beautifying" it. Here: tell Finder to come to front 
tell application "Finder" 
activate 
end tell

tell application "Remote Buddy" 
-- Say something really intelligent ;-) 
say "It's really dark here"

-- Give the Finder an additional 0.5 seconds to achieve 
delay 0.5

-- Fade in from black in 0.5 seconds 
visualize effect "fadeIn" for duration 0.5 with color "black"

-- Tell the fade engine to clean up 
visualize effect "fadeCleanUp" for duration 0.0 
end tell

Best regards, 
Felix Schwarz