On the STS download page, you state not to use the Cocoa version as it has issues.
But on the other hand, the Carbon version is really unusable on Snow Leopard, as the Java Source Editor view is broken (e.g. you don't see breakpoints, screen gets garbled if unfolding import section etc.)
Tested this on 4 different SL machines (3xMacbook Pro, 1xMac Pro).
The cocoa version doesn't have this issues, but sometimes Eclipse stalls.