I was just there visiting last week. Although I can't speak from personal experience (I worked for the government last summer), my general impression is that it is NOT a lifestyle firm. As I understand it, "lifestyle firm" implies a firm that has flexible working arrangements (i.e. part-time, work from home, etc.) such that one can both raise a family or pursue other interests WHILE progressing one's career. In this respect, I don't think many if any of the large NYC firms are considered "lifestyle." My talks with junior associates at Davis and Cleary divulged that 2,100-2,200 billable hours a year are not uncommon. Assuming you work 48 weeks a year, bill 80% of the hours you spend at the office, and work 5 days a week, that's roughly an 11.5 hour day. I think this sort of schedule tips the work-life balance in favor of work.
That said, Davis is widely regarded among its peers as being one of the "nicest." My short time there did seem to support this, and it's pretty well regarded by all my classmates who have summered and recently started there. This might be fostered by the lock-step schedule shared by both associates and partners, meaning that people aren't competing for bonuses or killing themselves to bring in business. So, in that respect, it does appear to be a more amicable work environment than some others...just don't expect short days. I think those are reserved for smaller firms and secondary markets.