Windows 7 ReadyBoost - What File System To Use With Flash Card/Drive?

Theoretically, for ReadyBoost to work as it should, you should probably stick with NTFS.

Really, NTFS is the way to go with any partition that works with Windows as long as you don't need cross-platform compatibility. NTFS support on Linux and MacOS is shaky and I wouldn't depend on it for mission-critical applications.

You shouldn't just 'pull-out' the SD card, or a USB-key for that matter. You should go down to your taskbar, right click on the Safely Remove USB Devices and select the device you want to remove.

This will avoid corrupted files and unwanted read/write interrupts.

tl;dr: Use exFAT instead of NTFS.

exFAT would definitely be a better choice not only for ReadyBoost, but for ANY non HDD type storage media.

exFAT is much simpler of a filesystem, and preforms less random unnecessary writes to the drive. Every single write to the drive wears down flash drives/SD cards/solid state drives/memory cards. Once worn out, they will no longer work at all and be useless.