Package management is a blessing when there’s integrated QA and support. apt-get is only one half of the equation; the Debian Bug Tracking system (and the people behind it) is the other.
Case in point: fink adds apt-get to the Mac OS, but the result is that updates from Apple and updates from fink compete/collide, and when there’s a problem, the natural result is finger-pointing rather than integrated QA.
Debian/ubuntu have scaled amazingly well, but they rely on quite a bit of trust. The MS Windows marketplace includes lots of mutually distrustful players, as does the Mac OS X marketplace. It’s not at all clear how apt-get and the debian bug tracking system (or ubuntu’s launchpad) can scale to support that sort of marketplace.
tags pending: software installation quality