It wasn't a choice for me. After graduating from Business School I struggled to find any work besides occasional short term contracts involving long, long hours and lots of travel, and even those have largely dried up. My wife had to go back to work to support us - thankfully we can manage on one income - so I became a SAHD by default.
It's difficult to describe how I feel about this knowing that some people would do almost anything to be in my position, but it's a mixed blessing at best. Sure, I get to spend all day with DD (now 21 months) and it can be very, very rewarding. I also have enough insight to realise that I am quite privileged to be part of her life at this age.
But it's hard work. We moved house when expecting DD so ended up in an area with no support network. The various baby/toddler groups and activities I've gone to have not exactly embraced my presence as a man, and I'm still coming up against things like change facilities in women's toilets. Going all day without adult conversation is mentally very challenging, and when DW is home - although she does much more than her fair share after working long hours in a professional job - she'd rather just enjoy playing Mom, so it's left to me to enforce bedtimes, boundaries and things.
But most of all it's a constant, depressing reminder of my inability to find employment of any description, never mind something commensurate with what I can actually do, and it's a signal to everyone else to judge me. I spent the thick end of US $100,000 on my MBA and frankly I'd rather be employed and earning considerably more than my wife so that she could go part time in order to spend more time with DD, which I know she wants.