I've been very much enjoying Matthew Freeman's blog lately, including this post on How to Quit Being a Playwright. The first point is my favorite, and the hardest part about doing it. It's actually easy to quit (in theory)--you just stop. And you don't need to tell anyone. You don't need to write a furious blog post, there's no paperwork to fill out, no HR person to notify. You don't get a farewell party. There's no one who recruited you into playwriting who is likely to be hurt that you're leaving. You'll be missed by some of your theatre friends, for a while, but not as much as you'd like.
I also very much like his recent post on Day Jobs and Staying an NYC playwright, too. (Which also connects to a nice essay on the same topic by Barbara Hammond.)