Motherboard manufacturers have really emphasized M.2 this go around with the new X99 chipset. Until now I really haven't cared, but as soon as I read that it raises the bottleneck of 6GB/s on SATA-III, to 32GB/s on M.2 (by utilizing PCI-E) boy was I paying attention! So my initial reseach has been very productive and I've grabbed a couple of links that helped me know what it is, and how to distinguish between the different types. THEY'RE NOT ALL THE SAME, so its important to know the differences! Each one has its own purpose/functionality.

Wikipedia gave a really great overview of its origin as well as a breakdown of the pin numbering, keying, and notches on both the motherboard and the M.2 module being inserted. Something worth mentioning is that "M.2 modules with two notches in B and M positions use up to two PCI Express lanes and provide broader compatibility, while M.2 modules with only one notch in the M position use up to four PCI Express lanes." 

1.You can read all about this here: http://en.wikipedia.org/wiki/M.2

Next, I wanted to know what the differences in Keys and Notches were, A, B, C, etc. The manufacturer of the M.2 connector released an easy to read and very simplified PDF that talks about connecter hight, card measurements (2242, 2280, etc) and module Nomenclature (ex: 2242-D2-B-M. This is good to know since places like newegg are still a little shallow on the details.)

2. That link is here, remember its a PDF: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&cad=rja&uact=8&ved=0CCkQFjAB&url=http%3A%2F%2Fwww.te.com%2Fcommerce%2FDocumentDelivery%2FDDEController%3FAction%3Dsrchrtrv%26DocNm%3D1-1773702-1NGFFQRG-EN%26DocType%3DDS%26DocLang%3DEN&ei=okw4VOTaEaze7AbOj4C4Dg&usg=AFQjCNE0w8gf7ojdMVBXgaxC-B2nz9F2RA&sig2=O7AKV-2tDR9_hsBVIKQgHQ&bvm=bv.77161500,d.ZWU

Lastly, I found a couple of videos on youtube that have great rundowns on what it all means for us as consumers, functionality, practicality, capability, etc.
3. -NCIX - https://www.youtube.com/watch?v=JVMVjyBA7Q0
   -Pauls Hardware - https://www.youtube.com/watch?v=Gx8fdVBs38E

So for example, EVGA's X99 Micro motherboard has an M.2 Key-E interface. The M.2 Key-E canNOT be used for storage devices, but for "wireless connectivity including Wi-Fi, Bluetooth, NFC or GNSS" only. For storage, you'll want M.2 Keys B or M, which EVGA currently only offers on the X99 Classified. Some modules and connectors use both the B and M interface too. Some of these differences are very minute, (sometimes by 1 or 2 pins!) and aren't that visable. 

BE AWARE that some motherboards DO actually disable one of the PCI-E slots when the M.2 connector is occupied. ASRrock x99 Extreme4 and Extreme6 do this. Here's the link to the manual: ftp://europe.asrock.com/manual/X99%20Extreme4.pdf , and the excerpt from the manual: "* If M.2 PCI Express module is installed, PCIE5 will be disabled." So to everyone thinking about using their M.2 slot on any motherboard, MAKE SURE you download and check their manual FIRST!

Please feel free to add on to this or correct it as much as possible to help our awesome EVGA community stay up to par with the coolest tech on the market!

Yeah, no prob! I do still have one question that I haven't found an answer to. Does the M.2 slot actually use the lanes from one of the adjacent PCI-E slots? If so, which one? And could this cause a bottleneck for either the SSD or the graphics/expansion card in the slot that its borrowing lanes from? I've downloaded a few manuals for different motherboards but none of them have any details on changing the location of expansion cards when the M.2 connector is occupied... So... maybe not?

VVhiplash
Yeah, no prob! I do still have one question that I haven't found an answer to. Does the M.2 slot actually use the lanes from one of the adjacent PCI-E slots? If so, which one? And could this cause a bottleneck for either the SSD or the graphics/expansion card in the slot that its borrowing lanes from? I've downloaded a few manuals for different motherboards but none of them have any details on changing the location of expansion cards when the M.2 connector is occupied... So... maybe not?

PCI Express requires a dedicated line so it can't borrow bandwidth from other slots, it needs it's own. That's how a serial point-to-point bus works. That's what I mean when I say some motherboards connect it to a SATA controller (so M.2 it doesn't use PCIe at all), others feed it a dedicated x1, x2, or x4 PCIe lanes. The hookup type is going to determine the max available bandwidth to the M.2 SSD.
 
Some newer boards (such as the ASUS Z97 Pro Wifi) will offer both SATA Express and M.2 slots but you can only choose to use one of them. A switch on the board detects which slot is used and routes the PCIe lanes accordingly which deactivates the unused port. Since there aren't enough dedicated PCIe lanes both can't be used. There's been a very wide variety in how OEMs have routed the M.2 slot hookup so it's best to always check the specific board in question.

Learned something new, for anyone who might come across this thread. (don't know if its dead already or not.) but some motherboards DO actually disable one of their last PCI-E slots when the M.2 connector is occupied. ASRrock x99 Extreme4 and Extreme6 do this.
 
Here's the link to the manual: ftp://europe.asrock.com/manual/X99%20Extreme4.pdf , and the excerpt from the manual: "* If M.2 PCI Express module is installed, PCIE5 will be disabled."

So to everyone thinking about using their M.2 slot on any motherboard, MAKE SURE you download and check their manual FIRST!

Burke888
Whiplash that you for assembling this information and getting it all into one place. You might want to edit the OP with your latest post just in case someone doesn't read the entire thread. I know I might have almost missed it and it was right at the bottom.
Thanks again!

Edited! Thanks :D

Great information for those that don't know.  

Not sure if this can help but i don't see a type E so i am a little confuse
I think the type "E" could be wless lan only or something like that i think is USB based connection but is hard to find a clear edge connector picture

bcavnaugh
So to say then on the X99 Classified Motherboard you cannot use any of the M2 Ports and run 4-Way SLI or install 4 Graphics Cards at the same time because of the PCIe Lanes?

Without looking at the manual and/or contacting EVGA, I'm not quite sure. It certainly makes since, if even the 5960x can only handle 40 lanes, and the M.2 slot is taking either 2 or 4, then you'd have to bump down a couple of your video cards to 8x if you were planning on 4way sli. I don't think EVGA disables any of their PCIE slots when M.2 is activated.