Ah, a topic near and dear to my heart.
My day job is running a marketing and brand strategy firm that I co-own, which means the normal long hours and stresses facing an entrepreneur. That said, writing is a priority and I'm lucky enough to have a very understanding business partner who gets that I am building my writing career.
Something I haven't seen really discussed here is that now that my book is published, I feel like I have three jobs instead of the old day-job/by night dichotomy. Now I get to work at my day job, be a writer who produces, and be an Author who markets and promotes her work while looking after her literary career.
Some days this seems easy-peasy. On others, it makes me want to crawl into the nearest cave and die. For me, writing is the hardest part. Promotion is very time-sensitive and concrete, as is the day job stuff, but writing falls by the wayside unless I am very rigorous about goals, tracking, self-imposed deadlines, and fun stuff like general discipline.
Another complicating factor (I know, I'm a special snowflake): my day job involves a LOT of writing. Sometimes it can be hard to switch gears, but I find that having a few rituals around my writing and being willing to put down the day work in favor of my dreams works wonders.
Thanks everyone for your input; I'm really enjoying this thread!