Most MacBook users are unlikely to ever employ the combination digital and analog audio input port, which has appeared on all Mac notebooks for years. Podcasters are likely to use a USB mic like the Blue Snowball instead.
However, lots of users are likely to want to use their iPhone or iPod touch combination headset/mic with their MacBook for video conferencing, and recent notebooks have added the additional pin required to support recording audio in addition to stereo headphone analog outputs and digital audio output.
Dropping the rarely used audio input jack helped enable Apple's engineers to include a new SD card slot for accommodating SD, mini SD and micro SD flash RAM cards from cameras and other devices. The new port also appears to supports the SDHC (Secure Digital High Capacity) standard, which allows card capacities up to 32GB.
Support for FireWire 800 is also new, signaling a return to the ubiquitous FireWire Target Mode feature that has long defined the Mac experience. While capable of speeds theoretically twice as fast as standard FireWire 400, the FW-800 specification uses a different plug to accommodate extra wires needed to support faster speeds with FW-800 devices. It is, however, backwardly compatible with FireWire 400 devices and only needs a simple FW-400 to FW-800 cable to work with existing FW-400 hard drives and other devices.