She taught full time for 3 years, and burnt herself out with 70 hour weeks of planning, marking, parental communication, and miscellaneous bureaucracy.
Now she's working as an on-call substitute, working 8:30-3 whichever days she wants, and (get this) making more money than she was teaching full time.
Although I definitely see the advantages of the stability of knowing who your classes are, sick and long service leave and paid holidays over the freedom from preparation, marking and report writing and other paperwork. I think being a substitute teacher you miss out on a lot of the benefits of the actual teaching too, like building a relationship with your students, and being able to teach long-term concepts instead of a period at a time.
One of my co-workers makes most of her living from substitute teaching (she teaches a part time load) though and seems to be fine with it, so different strokes I guess.
She does occasionally get longer-term assignments for teachers who are away for a couple weeks at a time, so there's a bit of relationship-building and long-term-teaching here and there. She also likes that she has a less authoritative role and can relate to the students on a friendlier level.