According to commenter Erin, the Spot and Leopard tools from Spitzer don’t work on OS X 10.5 due to a Java issue. I haven’t tested this myself but I’ll try to verify this evening when I’m back on a Mac running Leopard (and Leopard, boy that’s confusing.)

There have been conflicting reports about Java on Leopard. Many have complained about a lack of Java 6, some have said that Java 5 is broken too, and others have said Java 5 works just fine. The Spitzer Science Site itself is saying:

Spot and Leopard have not yet been tested under Mac OSX 10.5 (Leopard). We strongly recommend that users not upgrade their OS prior to the Cycle-5 proposal deadline.

That seems like very sound advice.

Update I just tested Spitzer Leopard, seems to work fine in … Leopard. Spot seems to work too, but I did not in anyway test in rigorously. I wouldn’t upgrade before the proposal deadline, just to be safe.