I am getting the message "There is nothing to install." (Mac)
If you ever see this message after trying to reinstall your PowerMate software, it means there is one more file standing in your way.
Go to your Home folder (house icon) and go to Library>Receipts. Delete the PowerMate Pkg file and all should be well.
On Lion and higher the Library folder is hidden, so you'll need to go to Finder>Go>Go to Folder> ~/Library