Just thought I'd pass this on FWIW. I have a shareware Applescript 
application ("CopyDrop") which runs under Tiger but broke under 
Leopard, which I finally got around to testing. The idle handler was 
the culprit. It turns out that the only issue was that Leopard didn't 
think it was a stay-open application, so it never idled at all... 
This is really odd, especially since it was read-only in an 
application bundle. Once I recompiled under Leopard and re-saved as 
stay-open, all was well.