Thank you, Andrew,
For most modern hardware, this isn't an issue, but for slower hardware (e.g. mine), or for power-lean systems (e.g. the OLPC) I think it could be.
The soundStopWhenDone preference is set to on in the OLPC Etoys image, FYI. When the user switches away from Etoys, we also shutdown the sound system.
-- Yoshiki