A lot of people seem to be misinterpreting the post and are assuming 37signals are promoting sloth, inactivity or doing things more slowly. As a company that releases products and new features on a pretty regular basis, 37signals should not be accused of this.
Instead, the post is actually highlighting the problems caused by "urgency." Urgency can be a massive problem because most non-emergency matters of urgency are bred by laziness. This is because people have asked for tasks to be done by a reasonable deadline in the past, but then the job hasn't been done due to laziness. So.. the next time the person asks, they make the job look "urgent" to force it to be done on time. After several cycles of this, almost everything becomes "urgent".
Consider the way many people complain about and at corporations. Their anger and demands are way out of line with what happened to them (some bad service, maybe) but most consumers know that most big companies simply won't listen unless you make a disproportionate amount of fuss.
This is the sort of urgency that is very harmful to SMALL companies and freelancers. It's those clients and customers who claim every tiny job or feature is URGENT when, in fact, it's not at all. Those clients are the ones that cause stress and the ones that will ultimately give you a heart attack.
There is a two way relationship needed with compromise on each side. The clients / users / customers need to be reminded that only emergencies are urgent, but your compromise is that if you promise something then MAKE SURE YOU FULFILL IT! I'm sick of how many supposedly "reliable" people don't live up to their promises.. yet we're supposedly meant to accept this nowadays. Well, I won't, and I'm with 37signals on this one. Ditch urgency, live up to promises, and it'll all go a lot smoother and with less stress.
Fulfilling promises is about as much about which ones you make than what you do to make them happen once they're made.
"Your failure to plan, does not constitute my emergency."