I actually made an online course with some of my basic "tech knowledge". Now if a friend asks me, for example, about the process I went through to create a Facebook application, I send them to my course. I obviously won't charge my friends for the course.

I still get questions like this and have recently started to refer my friends to Quora.

Ultimately, as you mentioned, the overall lesson is to learn how to say 'no'. You can do this with respect and tact.