So for the situations I tend to end up in, one-on-one interviews, conversations in front of a white board with 2 or more people and sometimes a group chiming in with opinions. here are some ideas with regards to wired, wireless, digital, number of inputs, where to record and so forth.

Insight number 1 — tracks

A video camera usually only has two sound tracks. If you want more mics than two, you will have to record those on a different recorder, being it a camera, a dedicated recorder or a sound card connected to a computer. This means that you need to do synchronization. Unless you are fancy with SMPTE or something, that will be done by matching audio automatically. If you already need to do that, it does not take much more time to match many tracks algorithmically.

Insight number 2 — synchronization

If you already accept synchronizing multiple sources, you might as well have the recording device on the subject. The exception being that two mics should be wireless and their receivers should be mounted on the main camera to get sound and images in lockstep.

Insight number 3 — lapels don't scale

It's a lot of work to mic people up. Well, not a lot of work but it does not scale to when you have 12 or 50 people. A handheld wireless mic which can be passed around can be a good option in those cases. Also, everyone understands how a normal handheld mic works, so don't go for one where you talk at the side of it or something. You could also use a portable recorder for this with built-in mics. Actually that may be the best option.

Insight number 4 — no digital

No need to go digital. It makes more and more sense in our day and age to go digital from the mic to the recorder, but since most cameras don't have digital sound inputs afaik, you'll have to wait for that for a while. And for your other devices, if one believes this blog post's insights to be true, you'll use portable recorders on the person, which come to think of it is kind of all digital, just a very short chain.

A possible setup from these insights

• Two wireless lavalier/lapel mics with the receivers mounted on-camera. You could go with just one and use the other channel for picking up ambient sound for synchronization
• Any other cameras used, can take up sound from any fixed mics, including boom mics, indeed they should use this to get some synchronization signal.
• Two people can be be mic'ed up with the wireless mics,
• any others can be mic'ed up with lavalier mics that go to a recorder directly on the person's body.

Being a bit more concrete

A. One wireless lavalier mic for the main camera,

for example Røde rødelink newscaster/filmmaker (untested by me).

B. More lavalier mics

All other lavalier mics used, would have their own recording device on the person's body. Here you would need to find good but affordable such recorders, or use mobile phones.

• Sony has an apparently great little mobile recorder under €100, the Sony ICD-UX560, but ideally you'd want to go a bit cheaper than that. Also, it does not come with a clip, but it does have a mic input with bias (3-5V for electret condenser mics).
• A mobile phone with e.g. the aputure a.lav mic. I have that one and I don't like it, though.
  

  I suspect some mobile phones apply compression, maybe there is a way to avoid that. Record that note App works well on Android as a recorder in my experience.

There are some novelties in the field, such as the

• Sennheiser Memory Mic, but I wish it came in black and not white. It's also at ~€200 a bit on the expensive side.
• Same price range for the Tascam DR-10L Digital Audio Recorder with Lavalier Mic .
• There is also the Zoom F1-LP, with lavalier mic, roughly the same price.

C. One handheld microphone

One handheld microphone that you can use for non-mic'ed up people to speak through. Here is a recorder that is of interest for this:

• Tascam DR-10X Plug-On Micro Linear PCM Recorder (XLR). Aroung €100.
• Here is one that even supplies 48V phantom power: Saramonic SR-VRM1 Plug-On Linear PCM Recorder for XLR Microphones, around €125.
• You could also use a handheld voice recorder such as the Sony ICD-UX560 (again) as a handheld microphone.
• Or even use a mobile phone, possibly with a mic sticking out to make it obvious where to talk. Make sure to have a good screen lock, but not so good that you can't unlock it because the finger print holder went to lunch.

Risks with this approach

• Uneven sound quality with so many different recording devices.
• Synchronization not working due to sound images being too different between different mics.
• It's hard to know with confidence if a local device is indeed recording. With a central mixing desk you could check. Maybe if you use phones you could have them report over the Internet their recording status.
• People wandering away with the devices.
  If a person wanders away with a wireless mic, you lose the mic. If he wanders away with a recorder however, you also lose the recording from that person! And you will have to edit them out of the video. A fitting punishment maybe :).

Go full insight— No wireless mics?

Actually for when only two subjects need to be recorded, two wireless camera mounted systems might be the best choice. Maybe one should never go go full insight, but you could probably get away with only portable recorders on the subjects, and sync up via the cameras' built-in mics. Actually for when only two subjects need to be recorded, two wireless camera mounted systems might be the best. But, you could probably get away with only portable recorders on the subjects, and sync up via the cameras' built-in mics.