I've seen one and a half startups fail because of this. (The second one isn't dead yet, they still have paying customers, but they were losing significant amounts of time to fixing regressions and incurring corresponding customer dissatisfaction.) For that matter, I've noticed that Reddit's had many more regressions lately, and that things that used to be rock-solid (eg. pagination) now seem to break disturbingly often.
This article made me suddenly realize that news.YC does not have a "Send to a friend" feature!
I did not realize, until you said that, how much time I've been spending emailing article links + comments links to my friends who don't yet read Hacker News. This feature would be a great help!