One day, a Gnome update breaks all plugins, in one case making login in X impossible unless you manually deactivate stuff using the shell. The next time, a kernel update makes sound stop working after waking up from standby. It's mostly small regressions, and they usually get fixed a week later, but something temporarily stops working at least once every 2 months.
However, Arch also makes it much, much easier to run recent versions of, basically everything. You never have to fiddle around with 3rd-party package repos, you just install stuff and it works. It's how package managers are supposed to work, but not the experience I've ever had with Debian and Ubuntu. Of course, the fact that Pacman is fantastically fast compared to apt doesn't hurt either.
I love Arch. In aggregate, I think it prevents more headaches than it causes. But you have to be prepared for some unexpected problems and fiddling around.