Hi Neil,
We still haven't tested the new version of PixInsight 1.8.0 for Mac OS X 10.6 compatibility. You can try to run it on your machine. Just make a copy of the old application, just in case. Anyway, the previous version, which has verified compatibility with 10.6, is still on the software distribution server, so there's no risk at all because you can always go back to the version that you have now.