Since a few people have asked this over last couple of days: Yes, the current version of Lighthouse has been well-tested on Leopard and is Leopard-compatible.
That’s the reason why we did not release an update specifically addressing Leopard, since Lighthouse is already compatible with it. Just make sure that you are running the latest version of Lighthouse by clicking the “Check for updates…” item in the main menu.
However, some users had trouble getting Lighthouse to run on their Leopard installation, not caused by Lighthouse itself, but by third-party system modifications that were not Leopard-compatible yet. If you experience issues with Lighthouse on Leopard (specifically, the Lighthouse icon not appearing when you launch it), please make sure that you do not have any third-party system modifications installed (so-called “Input Manager” hacks) and that there is no legacy application auto-launched via your “Login Items” (You can access your “Login Items” by selecting your account in the “Accounts” view in “System Preferences” and clicking the “Login Items” tab. Just remove all items unless you are absolutely sure that they are Leopard-compatible). Once the problematic tool is removed, Lighthouse will run perfectly on your Leopard installation.