Breaking Into The World Of Kernel Hacking?

crow_t_robot asks: "In the past couple of months I have become increasingly interested in kernel programming and have finally decided to take the leap and 'get my hands dirty.' I have searched around the web and read a few docs and FAQs on getting started with the kernel but I was wondering what kind of personal experiences those in the Slashdot crowd have had that are so bold as to start goofing with the kernel code. For those that have become competent kernel programmers, how did you 'break in' and what advice would you give beginners?"