Nonetheless, "the udev debacle" refers to systemd merging udev into its codebase, along with tying it to systemd's shared files, the recent "debug" parameter fiasco and the rather blunt statement by Lennart concerning migrating the transport to kdbus: http://lists.freedesktop.org/archives/systemd-devel/2014-May...
PulseAudio (originally PolypAudio) is a networked sound server most often used in Linux systems coming with a variety of centralized features (see here: http://www.freedesktop.org/wiki/Software/PulseAudio/About/), which proved to be highly controversial initially and less so to this day. People realized it was buggy and unstable, and different factors were blamed: poor integration, sloppy ALSA drivers, or PulseAudio itself. The most common narrative these days is "PulseAudio was bad because Ubuntu rushed it", but I haven't studied things in enough detail to pinpoint exact reasons.
As for HALd, it did solve problems at the time, but I'll quote the Ubuntu wiki: https://wiki.ubuntu.com/Halsectomy