The only replacement I've found is to go back to using Watson from Karelia Software.
(Sherlock 3 with 'web services' was supposedly based on it, Watson won the Apple's 2002 'Most innovative product' award).
It does a similar job to Sherlock but it doesn't have a flight tracker: I have to use widgets for that. 😟
I just wish Apple would release a download of a 'Sherlock for Leopard' App... It was such a useful app and I really miss it.
Watson however is good at what it does and I hope it will be useful to everyone...
It is now a free download (It was killed off when Sherlock 3 was introduced) and it is available at
http://www.karelia.com/watson/
I've had no problems with it so far in Leopard even though it was for OS X when it first came out... (Sherlock 3 came in 10.2)
Hope it will help you as it has helped me!
JimBob101