Causes a pretty big 200MB+ memory leak and 30% extra CPU usage when writing a mail (not viewing or using gmail in other way) and does not perform it's advertised function.
I tried your script with all Gmail versions and no sound came up.
Please fix it.
Like others, I've tried a number of things to get this to work, but it simply does not produce a notification sound as it should. This has the potential to be a great script.. but alas.
I'll look at the source later to see if I can get it working.