The Leonardo was my first Arduino, I bought it because it's native USB capabilities. After experimenting with Arduino, I decided to migrate from my Arduino Leonardo to a standalone Atmega328p or, for smaller projects, to a microcontroller from the Attiny family.
After some research I found this guide by PeterVH: http://petervanhoyweghen.wordpress.com/2012/09/16/arduinoisp-on-the-leonardo/
After several failed attempts, I was able to burn the bootloader and upload sketches successfully and wanted to share that with this Instructable.
I can not be held responsible for any damages that could occur to you or your equipment while following the procedures present on this page. Also, I give absolutely no warranty on the correctness and usability of the information on this Instructable. Please note, however, that these procedures have worked in my case without any damages or problems.