There is this really horrible iMac I have, and could not get it going online for a year or two. One night, I trouble shot the hell out of it and now it can browse online.
Setting up my HTTP server and BBS were kinda hard. Took a few hours to get it all configured.
Having Telephone, Cat5, and cable running into every room in the house took some work.
Making things run on batteries
Softmodding the XBOX (It was a big deal for me)
Fixing my PS2.
More to come.