I haven't tested audio just yet, but here's my view of what happened graphically after modifying the WSEGL_UseHWSync setting:

The scrolling in the application manager view is indeed smoother. However, the drawback seems to be that it doesn't scroll very long per each thumb slide. Maybe that's why the Nokia devs left that setting off because of the earlier complaints about the slow scrolling.

I was looking around for something else to have improved in hildon after this setting, but cannot really see anything else that sticks out besides the application manager view. The scrolling when switching desktop still has some slight stuttering and the same goes for listviews in for instance the email application I think.
Anyone else seen any other differences?