Currently work-in-progress, more questions/answers to come
Q: I can't save my game on Android (File I/O Error, etc.)
A: On many newer phones/tablets running Android 3.0+, you'll have multiple storage devices available like internal flash memory and SD card slots (paths like /mnt/sdcard and /mnt/sdcard-ext). Unfortunately, the OS may only permit 3rd-party apps write-access to one of these devices so saves will fail if using the read-only device. Try moving your games to each storage device until you can save without an error.
Q: I can't save my game on iOS (File I/O Error, etc.)
A: Your game directory or save files have read-only file permissions prevent the app from modifying them. Use SSH or iFile to add write access or change the file owner to "mobile". The exact command when logged in via SSH is "chown mobile MyGame.sav", or for a whole directory "chown -R mobile MyGamesFolder/" (replace MyGame.sav and MyGamesFolder with your own filenames).
Q: I can't save my game on WebOS (File I/O Error, etc.)
A: You're using a broken OTA update of WebOS 1.4.5 and the app cannot modify any files in /media/internal. There are some workarounds if you use Preware, but the clean way to solve this problem is to use WebOS doctor and re-install the OS (make sure to back-up and important data beforehand).
Q: I tried to copy a new SRAM/battery save file (.sav, .srm, etc.) but the game still shows the old save contents.
A: When using auto-save states (the default) on most systems, SRAM is usually loaded from the state itself. As a result, you should temporarily disable auto-save states under the system options or delete the auto-save state file as you replace the SRAM file. Once the game performs a clean boot from the beginning your new save contents should appear.
Q: I have input lag or low framerates on Android even though my device has a very fast CPU
A: There are many variables affecting Android performance, especially the device's graphics drivers. Try the following items in order and check for changes in performance after each one:
Q: How can I fast-forward the emulation?
A: There are touch-screen and hardware key methods to enable fast-forward (actual speed depends on how fast your device can run the system, up to 4x):
Q: I already bought an app for one OS, can I transfer my purchase to a device using a different OS?
A: Sorry, currently there's no means to transfer licenses between the various app stores so you much re-purchase the app on each service you use (Google Play, Cydia, etc.) to get automatic updates. However, all the apps are DRM-free so you can install them on as many devices as you have running on the same OS.