I like getting growl notifications of new tracks being played and I missed this feature when I started to use Google Play instead of iTunes. I wrote an NPAPI browser plugin to create a javascript->Growl bridge which you can find here, this extension uses that in order to send everything off.
Big thanks to asavartsov for the cloudplayer-scrobbler source which originally, saved me a lot of time. I have since moved on to a different style of getting the playing track information and stopped using any of his code.
(The MIT License)
Copyright (c) 2011 2012 Nicholas Letourneau ( http://nicholasletorneau.com )
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.