I have the G1 and current. It is a good deal providing we are talking base camp. I have slept warm down to the teens, but if you are a big guy they are cut tight. I have my issued down/poly fill as well. No I'm not that old, they were still issued in the 90's. I paid $100 for mine as Aron said on eBay. I say go for it if not planning to pack it.
I saw them on a thread with another web site I figured I would ask here with the members here are a little more hardcore and tend to know their stuff a little more. I kinda liked the fact that they fit together but if it is a POS. I guess if you look hard enough you can find them for around $100.
I have one. Like Aron said, they're heavy and bulky. I don't think they're all that hard to put together and use as a system, but that's just me. Most of the time, I'll just use the green Patrol bag and can take that down into the 30's by itself (used it just last weekend down to 37 and was plenty warm with just midweight long johns...but I do sleep pretty hot though). I've used the bivy and Patrol bag down to the upper 20's before. My Patrol bag weighs 2lbs 4oz, so not terrible, but not the best by any means. I think the black bag is somewhere around 4lbs and close to another 1.5lbs for the bivy.
I used one for a few years as well and it is very bulky. Both the green and black bags combined with the bivy take up the bottom half of your pack even when stuffed very tightly. I have been much happier with my marmont helium.
I use the bivy with any number of other bags including my Kifaru 0 degree bag. I have used it but as all have said super bulky. And I think the entire thing weighs in between 7-9 lbs, way too heavy.
I also used it in the army. I have a bad taste in my mouth for that system but if its what you can afford then its not the worst system you can spend your money on.
I also used one when I first joined. They are a good base camp bag, but that's about it. To heavy and bulky for anything else. I use my Mountainsmith bags with the bivy or my modified poncho liner and the bivy. Much lighter and way less space taken up in a pack. I have two full systems sitting in my garage, just in case the power goes out.