How do I increase flying speed?

You actually can in Minecraft mac/pc using mods like better sprinting, zombie's fly mod. If you are running a bukkit server you can download CreativeFlySpeed as a plugin to speed it up

You can actually increase it with mods in pc/mac.
Mods that will increase your flying speed:
Better sprinting
Zombie's fly mod

You can sprint in PC / Mac, just like any platform version of Minecraft. You can also sprint, then fly (double jump), to fly faster than normal speed. Just like on Console versions. Also, on PC / Mac you can hit the sprint key (ctrl by default, & editable via the in game options).

Sinfully yours,
:3V1L: Mr.J0K3R

You can sprint in PC / Mac, just like any platform version of Minecraft. You can also sprint, then fly (double jump), to fly faster than normal speed. Just like on Console versions. Also, on PC / Mac you can hit the sprint key (ctrl by default, & editable via the in game options).

Sinfully yours,
:3V1L: Mr.J0K3R

There is a command that works well, if you have commands on the version you are using. Here is an example: /effect RandomGuest speed 60 180. This gives RandomGuest speed 180 for 60 seconds.