Recording conference calls for multiple host podcasts has always been pretty much a huge pain in the ass. In particular, in the early days, this could not be done without multi-channel audio cards (or multiple audio cards), a hardware mixer and a whole messy bunch of cables.
Things have always been a little confusing on the software side: depending on the operating system there is the chance to have software mixers performing the same task as the hardware one, but they usually require applications to explicitly support their API/communication protocol (e.g. JACK on Linux).
Furthermore, even in the case that the audio protocol is standard for the whole system, the application may not support per-caller streaming, which makes editing and mastering the levels in post-production extremely hard (although there are some tools, such as Levelator, that help in the task).
Now we all have an open-source, multi-platform alternative (runs on Linux, MacOS, Windows), and its name is Mumble.
Mumble is born as an open-source, standards-based, low-latency, high-quality Voice-over-IP communication tool for gamers: as opposed to common alternatives such as Ventrilo, Skype and TeamSpeak that are instead closed-source (TeamSpeak had a particularly bad history of slow upgrades).
While open-source is nice and everything, Mumble was not better suited than the rest of the pack when it came to podcasting, it actually was a little worse than some of the competition (there are multiple plugins for Skype that allow call recording).
But Mumble does now have a trump card to play: since version 1.2.3 it allows to record the conversations going on a channel in a server, either as a mixdown (one file for the whole conversation) or using one file per participant.
Not only that, but multiple recording formats are supported: PCM uncompressed (wave), AU uncompressed, FLAC lossless compression, and OGG lossy compression.
The beauty of it all is that such freedom of choice also allows older, or low-power systems to be used as recording stations; while one would require a fairly powerful system to record a party of 10 in FLAC, I was able to record an OGG compressed multi-channel discussion between me and a friend on a 1.5 GHz Pentium-M with lots of headroom.