Can I speed up the Leonardo bootloader?
Detailed instructions on how to shorten the bootloader time of Leonardo etc. are explained [here] (as stated by @Chris Stratton).

The crux of the matter was to redefine the timeout period

/* ./arduino/hardware/arduino/bootloaders/caterina/Caterina.c */
#define TIMEOUT_PERIOD 8000


to a lower value.

However I do not have such issues with Leonardo it boots very fast.
So this issue depends on your environment.

There is also OptiBoot, an alternative bootloader that really boots faster link: