A good post Jackula. We had PD put R2.5 sound screen between our floors. They don't do it often, and we're really glad we paid the money for it, but there were lots of issues getting the contractors to install it properly. From memory, it took a lot of jumping up and down by us and then our SS to get it done properly. 4 times I think they had to come back and do it to make it 'work'. If we hadn't inspected it, and known the standards, the $2.5k we paid would have been useless as there were so many gaps with much larger than necessary ones left for down lights/plumbing etc.
So I guess what I'm saying is... Definitely do it (as well as thick underlay), but make sure you +/- your independent inspector ensure it is installed to standard!
KDR Chadwick 41 Eastern Suburbs