Are you referring to sets like the Scala G4?
If so, myself and several friends have been using them for a few years now... I forget the actual number, I think it was in the 1.5KM range though. Various conditions will affect this however, including whether riders all have the pop-up antenna up or not, and position throughout the group etc.
You can use them in VOX mode which will open/close channels between riders automatically as they speak, and you can pair up to 4 riders together (actually I've had 5+ in some cases, but that's not officially supported and is very glitchy.) My understanding is the new G9 units support up to 8, with limitations. Even when you have 4 people all riding together who are paired up, it is possible to open a channel directly with one rider out of the group, or all riders, etc.
A side note: While useful when they work well, the Scala units are pretty horribly buggy at times. The most frequent complaint I hear about them is that one, or even both sides of the headset will randomly die for no apparent reason. This has happened to me in the past, and I just recently picked up a brand-new G9/G4 headset unit which had a dead left side earphone right out of the box. So if you do get a Scala, despite the fact they're probably the most popular/common units in use, be prepared to deal with problems from time to time.