I am currently working with NR/G5 on my development system. I currently use NR with Homeseer on my production system with my Now Playing skin. Using the hsGirder plugin for Homeseer allows me to control and get status from Homeseer into my GUI interface. So with a little work using Netremote Designer you can build skins for NR which can be anything you want them to be as a GUI frontend.
I know there are people working on a Powerhome plugin for NR right now also. One advantage of NR is that its fairly lean and fast and runs quite well on older tablets like the Fujitsu 3400.
So Netremote is the GUI side of the solution. Mediabridge also comes with Netremote. It allows you to control media players. The best being J River Media Center. JRMC supports distinct zones seamlessly. NR and Mediabridge are tightly integrated so its a breeze to get that up and running. NR also supports client/server strategies. I have 4 clients around the house to control 5 zones. NR skins also run on a PocketPC so you can roam around the house browsing your music library and controlling your lights.
Girder 5 is the latest beta of girder. It has come a long way towards being a HA application. I and others have been working with Promixis to help them understand what is needed for HA users. Currently its fairly robust although still a bit buggy. I see it one day being as good as some other HA packages. Girders legacy strengths lie in its ability to control just about any other application on any PC on your network. Very powerful.
They are two parts of an integrated HA solution.
You can check out my threads to see my work.