Apple's AirPlay is confined to the use of iTunes on a Mac (pre-Mountain Lion) and a PC, ie. your other applications are not AirPlay enabled by default. This means that audio applications, games and streaming services such as Spotify, Pandora etc. will not be able to initiate an AirPlay stream to your AirPlay speaker.
There is however a very elegant solution to this problem in the form of AirFoil, a third-party software utility that enables ALL your applications on your Mac and PC to stream AirPlay audio to your Libratone AirPlay speaker. The company behind AirFoil is Roque Amoeba, and their website with all the details is here. The cost of AirFoil is approx. 25 USD, and you can buy it directly at the site.
When watching movies on your computer you should use the Airfoil Video Player (included in the license fee for AirFoil). This ensures that local video and remote audio always stays in sync. The player supports many video formats, including Flash and Silverlight web video, as well as basic DVD playback.
Note: As from Mac OS X Mountain Lion - AirFoil is not required anymore on the Mac platform (read more in the post above). Older Mac OS X versions still require AirFoil for system-wide AirPlay streaming.