Here is an attempt at updating the some of FAQ, to fully incorporate 1.08 features, or just to be more clear.
Changes are in bold italic. Comments in italic.
Q) Does download play work?
A) Download play
(single cart multi-player) works on most games and fails on others, most notably Nintendo franchise games (Mario, Metroid etc). This is because of the way the original cart's secure part of the ROM is implemented. A R4/M3s download play compatability chart can be found
here.
I've heard that the compatibility is better if the DS without the cart has flash-me. The only logical reason I can think of for that is that the RSA signature checking is disabled. I've never really understood the secure part of the DS cards, but I'm guessing that in this case the DS is sending the unencrypted form of the download binary to the other DS, and the original sent the encrypted version. Thus the RSA checksum does not match, but flashme'd DS's will ignore this.
A few of the games on the compatability list mention problems with multi-cart play. I have absolutely no idea what is going wrong there. The above question should be updated to address these things.
Q) What is the best MicroSD card for the R4/M3s?
A) Toshiba or Kingston-JAP (i.e. made in Japan, model number: SD-C01G) is the most compatible card for R4/M3s if you want to play
Castlevania - Portrait Of Ruin. If you dont play it, any other card will work fine with the other 1000+ games on
the "list". Sandisk Ultra2's is also likely to work ultra flawlessly with POR, but the price is ultra absurd (double the price of kingston). PNY/Viking also
OEM from the same factories that make the kingston silicons,
but there's no guarantee that these cards are
exactly the same as the kingston ones. There's a
chance that the taiwanese cards made by all companies work flawlessly with POR, but like I said, it's only a chance. Or you could buy any MicroSD you want, and buy the original POR game. After all it is only one game (imho, isn't that good), and probably a small glitch in the dumped backup. For a list of POR compatibility click
here.
Important: At the end of the day, the better cards
don't guarantee CV

OR compatability, but
only increase the likelihood that they will work and this is due to variable manufacturing quality.
That answer is pretty good, although there are a few other games with minor problems (generally not cauing playability problems) on the slower cards, besides the infamous CV
OR. The answer ought to mention that.
Q) Does the R4/M3s support multiple saves?
A) No. The only way to do it is to have multiple copies of the ROM either a) in different folders or b) with different names, to ensure a different .sav file is created per ROM.
Recent firmware versions have a feature to keep a backup copy of the save file, but still does not have full multiple saves support
--------------------------------------
A new question:
Q) What does the Slot-2 option do?
A) Originally, the Slot-2 option would simply cause the DS to boot the slot-2 device in DS mode. In recent firmware versions it will still boot flashcarts with a DS bootsector in DS mode. All other carts (flashcarts without a DS bootsector or original GBA carts will be booted in GBA mode using the image file '/_system_/gbaframe.bmp' as the frame.
I'm not sure if it uses the firmware setting to decide which screen to use for GBA mode, or if it is hardcoded. If anybody does know that, it should be added to the above question.
Disclamer: I do not (yet) actually own an R4DS.