Q 1: I don’t know which system each libretro core is supposed to emulate. A: Each libretro core is named for the emulator it is derived from, and you’re encouraged to check out the parent project. For example, libretro-snes9x-next.so is derived from the popular SNES9x emulator, while libretro-mednafen-psx.so is derived from Mednafen’s Playstation (PSX) emulator. Unlike other emulators (particularly on Android) that attempt to obfuscate the source of the emulation code–often so users don’t realize they’re paying money for free, open-source code–RetroArch encourages its users to be aware of the original authors whose hard work went into creating these great emulators.
Q 2: Why are the touchscreen control overlays so ugly? A: The devs know more about programming than graphic design. However, RetroArch is unique among its peers in providing a simple format for users to create their own fully customized touchscreen overlays. This format supports images up to 800x800 pixels (UPDATE: up to any size), variable transparency and user-defined hitboxes for each button. If you don’t like the way an overlay looks or performs, you can make your own from scratch or by modifying the ones that come bundled with the program. If you make something awesome, feel free to share it on the forum: http://www.libretro.com/forums/viewtopic.php?t=239
Q 3a: Why is RetroArch so laggy on my phone?
A: Well, this first depends on what kind of “lag” you’re referring to. Usually, people are actually talking about reduced framerate (i.e., sub-60 fps). In this case, the answer is generally: your phone is too old and slow for that libretro core. Try another, lighter-weight core and see if the problem persists. If all of the cores are having problems, you might have found an actual issue that can be addressed, so please make a post on the forum 
Otherwise, if you are getting lots of video stutters and audio pops, your phone may also be reporting the wrong screen refresh rate, which RetroArch uses to sync the emulator with the display (Samsung Galaxy S3 phones are a common offender). You can usually use a forced refresh rate (try something like 59.95 hz) or turn on ‘threaded video’ to fix it.
Q 3b: But libretro-pcsx-rearmed is faster than libretro-snes9x-next! That obviously shows that there’s something wrong with your SNES core and it needs to be optimized, right? A: PCSX ReARMed and SNES9x are structured completely differently and the systems they emulate are so different that trying to compare them is like comparing a Tyrannasaurus Rex with a banana.
Q 4: RetroArch emulates dozens of different systems. There’s no way this Jack-of-all-trades is as good as the single-system emulator I just paid $5 for. A: As a matter of fact, that emulator you paid for almost certainly uses the same emulation code as RetroArch, except that emulator’s author is charging money for code s/he didn’t even write, possibly against the stated wishes of the original author. We invite you to try RetroArch for yourself and come to your own conclusions.
Q 5: I have a crazy, obscure Bluetooth or USB gamepad that I really want to use with my phone. Will you support it?? A: Yes! You just need to use RetroArch’s built-in input analysis options to log what each of your pad’s buttons reports. You can post your logs in the pad support thread in the forum (device identifiers are CASE SENSITIVE!): http://libretro.com/forums/viewtopic.php?f=2&t=248 RetroArch also supports manual input binding, so you should be able to map your buttons that way, even if your controller isn’t automatically configured.
Q 6a: RetroArch would be absolutely perfect if it just had this one feature that only I want/need. Will you add it? A: Maybe. It depends on how difficult/disruptive implementing such a feature would be. Feel free to make a post about it on the forum but please don’t spam multiple posts in multiple threads and don’t beg. Also, if the devs say it’s not going to happen, please do not whine about it. RetroArch is 100% open-source, so if it’s that important to you, you can implement it yourself and submit a patch.
Q 6b: What if I offer to pay you? A: RetroArch is totally free and always will be. Bringing money into the mix causes nothing but trouble and resentment, and there’s no way we could track down and give appropriate compensation to all of the authors involved in the various emulation cores. Keep your money and be happy that so many individuals have worked so hard to bring you something great.
Q 7: I love RetroArch! Where’s the ‘donate’ button? A: See Q 6b. The only exception to this rule is donation of hardware for support on other platforms (see Q 8). There is also a ‘donate’ button on the forum to help pay for hosting costs but these costs are relatively minor, so don’t feel obligated.
Q 8: Will RetroArch ever be released for $MY_OBSCURE_PLATFORM_OF_CHOICE? A: Maybe! However, we can’t support it without access to hardware for the platform. If you would like to donate a piece of hardware, send a PM to Squarepusher or one of the other administrators on the forum or get in touch via IRC at #retroarch on Freenode.
Q 9: Other Android emulators have versions that are optimized for my individual device. Will you optimize RetroArch for my device? A: No. Device-specific optimization is a farce. They’re all using off-the-shelf systems-on-a-chip, anyway. Any “optimizations” are necessarily changes to the emulator cores, themselves, and almost certainly for the worse. In the case of specialized hardware, such as Xperia Play, that require special attention, you would need to donate hardware (see Q 8).
Q 10: I’m used to emulators using frameskip to give the appearance of full speed even on devices that are too slow to reach 60 fps. Will this be added to RetroArch? A: Not likely. Frameskip can cause (even greater) input latency and may interfere with some of RetroArch’s more advanced features. If you can’t reach full speed on your device, you’ll just have to get a faster device.
Q 11: My arcade ROMs aren’t working. I know they’re good, though, because they work with $RANDOM_MAME_EMU. What’s up? A: You almost certainly have an outdated ROMset. Most, if not all, other arcade emulators available for Android are based on extremely old versions of MAME/FBA, sometimes as old as 13+ years (with ROMsets to match)! RetroArch, on the other hand, uses a cutting-edge version of FBA that is in-line with the official desktop version(s). This means you get all of the sweet emulation improvements of a modern version, but you also need to use modern dumps. UPDATE: Since the inclusion of MAME cores, you’ll need varying ROMsets for those, as well: MAME2003 corresponds to the 078 set, MAME2010 corresponds to the 139 set and MAME2013/2014 uses whatever is the newest available set.
Q 12: I don’t see any Neo-Geo emulator. Will you add one in the future? A: Actually, FBA already provides excellent Neo-Geo emulation. Just make sure you are using an up-to-date ROMset (see Q 11) and have your neogeo.zip BIOS file in the same directory as your ROM.
Q 13: What about N64 emulation? You already have PSX emulators, so it should be easy, right? UPDATE: Got it covered! A: N64 and PSX are very different to begin with (see Q 3b), but yes, it’s in the works.