In the beginning we are just having a volume in MAFW that we were just setting to the GStreamer. This was a bit complicated to maintain because you always have to be careful of resetting volume to the pipeline when you create a new one and even after some state changes, meaning GST_STATE_READY for example, what I consider a GStreamer limitation, BTW. Anyway, we kept that with a conditional compilation because running Pulse was hell inside Scratchbox, at least for me.
Maemo 5 does not have global volume (to be changed by a user) and uses Pulseaudio, as I just advanced. It defines several volume roles so we can say that volume is context sensitive, meaning that call volume is not the same as multimedia volume, for example. As Maemo can have more than one media player it was not a clever idea to define our volume and use it with GStreamer pipeline and if you also take into account that you need to have the same volume as the status menu volume bar, mission turns much more complicated. The idea was then to use Pulse directly through ext-stream-restore2 API (which I think is not merged upstream yet). One of the side effect advantages is that we do not need to store the volume between executions because Pulse does.
Pulse API has the ability of several kind of loops, say, a threaded mainloop and a GLib mainloop. For simplicity and as it was enough, we used GLib mainloop API.
Other issue was merging requests implementation. We implemented this by sending only a maximum of 5 changes per second, it is once every 200ms in order not to flood Pulse with changes.
One of the things I did not like too much was the hacks to reconnect to pulse if they failed. In those cases we were just crashing, but people did not like it, so we had to implement reconnection (IMHO Pulse should never crash either). The issue was failures during reconnection, which made us to write a hack to try reconnection after one second, until we get it. This solved the problems but it is a workaround, not a solution (which should be Pulse not crashing or reconnecting always fine).
You can take a look at the code at mafw-gst-renderer-worker-volume.c and mafw-gst-renderer-worker-volume.h.