If anyone out there is using the Spaces feature of Leopard, you may have discovered that switching to IntelliJ does not automatically switch to the space it's running in. I found a work-around: simply open another project in a new frame, and then it will work! Cmd+tab, clicking the Dock icon - both will switch you to the correct space.
I've read elsewhere that this is a Leopard bug and occurs with all Java apps. I hope it gets fixed soon.