I got into modding when I decided to build my own Smurf at Uni. Damn thing is so unreliable. I don't even use it any more.
A couple of good rules with modding:

Never mod your main machine unless you really know exactly what you are doing;
Don't bite off more than you can chew: Some great ideas simply aren't worth the time, hassle and/or money;
Necessity is the mother of invention. Try and build something genuinely useful, or just make something look really cool;