Growl 1.4 is out with the first update in months. I welcome this. There were a number of SDK bugs that remained and I was concerned it had been abandoned. This looks like a good update. The preference panel received some much needed love.
The networking panel now provides an option to subscribe to alerts for a specific app on a remote machine.
There are some nice enhancements to the api. For example, URL callback has been fixed so that clicking on an alert can fire off a URL and allow the OS to figure out what to do with it.
Here's the version history for previous releases.