My complaint isn't about build times, it's about dark repositories which aren't just mirrors of offical repositories but also contain home-grown packages such as "Company X custom VirtualBox Ubuntu box for VMWare" which contains an Ubuntu machine with up-to-date guest tools for the version of VMWare we use, along with the versions of Puppet, NTPd, Samba, and so forth that we use for all our Vagrant-ified infrastructure. Thus we save time over building the guest VM from scratch (about 20 minutes for each box we spin up) but someone has to maintain that repository.