I decided to try converting some of my site designs to bootstrap recently, instead of having one of our developers do it. I haven't actually coded the HTML/CSS design on an entire page in 3 or 4 years now (not counting simple stuff) and this was light years easier than I ever remember. If responsive design is hard, your doing it wrong.
You built one very basic bootstrap site and despite not having done HTML/CSS in 3/4 years you've now got the expertise to tell everyone else they are doing responsive design wrong?
I've built responsive sites in Bootstrap, Foundation and "without a net" and I wouldn't presume to tell anyone what's hard or not about responsive design or even if I'm doing it right or wrong. Look if out-of-the-box Bootstrap is good enough for your needs (and more importantly your user's) awesome. That's called an anecdote.
