I happy to report that problems with Mac OS installation packages are now over!

The original issue was that Mac OS installer application has a well known and long standing issue (er "feature", as in "deal with it") of disregarding the default destination folder when a) the destination folder is the user's home directory and b) when the user runs the installer for anything but the very first time after rebooting the computer. However, I do need to install plugins in the user's home folder in order to enable the auto-update feature to work - otherwise the auto-update would fail due to insufficient permissions.

Finally, I have implemented a different approach, possibly the only approach that would work in the Mac world - instead of relying on the installer to put plugin files in the correct folder I now simply deploy everything to /tmp and then move everything to the user's home directory using a post-install script embedded in the installation package. Simple as that, but it took me several attempts trying to make the installer application to play nice.

If you had issues installing or running Mac versions of the mentioned above plugins, please follow the steps below:

1. Close Lightroom.
2. Re-download the installation package.
3. Remove plug-in folder in /Library/Application Support/Adobe/Lightroom/Modules. For example, if you are re-installing the Dropbox plugin, remove the DropboxExport.lrplugin folder.
4. Run the installer.

Now the installer should deploy the plugin package to ~/Library/Application Support/Adobe/Lightroom/Modules and set correct permissions.

I have updated pages with installation instructions for these plugins to reflect the new sequence of installer screens.
Let me know if any of you encounter any issues installing latest packages.Thanks!

October 9, 2012 Update:

A fellow developer asked to me to post the sample script I am using to install the package into the personal Library folder, so here it is (here I am using the Costco plugin as the example):

#!/bin/sh

if ! [ -d "$HOME/Library/Application Support/Adobe/Lightroom/Modules" ]; then
mkdir -p "$HOME/Library/Application Support/Adobe/Lightroom/Modules";
fi

# move the installation package from /tmp ($2) to the personal Library folder
cp -R "$2/CostcoExport.lrplugin" "$HOME/Library/Application Support/Adobe/Lightroom/Modules/";
rm -rf "$2/CostcoExport.lrplugin"

# assign the correct owner and set permissions
chown -R $USER "$HOME/Library/Application Support/Adobe/Lightroom/Modules/CostcoExport.lrplugin"
chmod -R 0755 "$HOME/Library/Application Support/Adobe/Lightroom/Modules/CostcoExport.lrplugin"

exit 0