I started playing with the Nokia 770 development SDK last summer and ported an old gtk+ 1 based game (xhyperoid) to the device. First I had to fix it up to use gtk+ 2 and then hildonize it. Not too bad, the first packages had some silly key assignment bugs, but that is now fixed in the latest version, available on maemo garage.
The original xhyperoid has also sound effect support but it's using old OSS and maemo only supports gstreamer or esound, there is no Alsa or OSS emulation available. Anyway, I'm planning on getting sound support in the next version.