Maybe this is common knowledge, but: since a default Projucer audio plugin project includes the juce_video module by default, it will add AVKit.framework to the XCode project. This will cause the plugin to not be loaded under 10.8 (regardless of the deployment target, there must be something going wrong w.r.t. weak linking). Removing the juce_video module, which is not usually needed for plugins, fixes this.
Thanks for sharing this - if it’s tripped you up then it’s bound to have caused trouble for many more people who didn’t post about it on the forum.
In general it’s a good idea to only select the modules that are essential for your plug-in/app.
I’ve just hit this I think. Maybe Projucer could spot this problem:)
I’ve just discovered that it’s possible to run old versions of OSX easily inside parallels though - so testing for this is going to be easier now:)