I've been working PT for 6 months now, as a consultant in my normal line of work (project management). Pros - flexible schedule, can work from home or from other locations, multiple clients means that everyone assumes I am with another client when I don't answer phone or email back right away. Cons - people do expect you to be available for in-person meetings on fairly short notice so long trips are not possible, income is not always predictable, once in a while I need to put in a full time workweek (up to 50 hours).
I got into it through a good relationship with a former employer, who was happy to contract out one thing that I did well, that they didn't have time to take care of.