Problem:
Sometimes in arch's repos there are some broken packages. They are often installed generally during update, so sometimes (because of many updated packages) it's hard to find which of them cause a problem. I know, fixing bugs take some time, but through this time many users may download the unfixed packages. In my opinion it is the main drawback of this distribution, so we must get rid of it. The number of downloads of the broken packages should be decreased.


Suggested Solution:

In my opinion this problem may be resolved by implementing package masking like the one in Gentoo Linux. There would be two parts of this mechanism. One in the repo, which allows repo's maintainers to block packages, for example via bugzilla. The other in the user system which let them to mask broken packages by themself on their system if only they notice some (and unmask blocked if someone want to).

Also system of downgrading should be implemented. If someone downloaded and installed a broken package it must be downgraded as soon as possible (I think this is moment of repos synchronization) if only previous version can be found (for example on user's disk). Pacman may also ask user whether it should downgrade the package or not (optionally add it to local unmask list not to ask in future).

This is _optional_:
If there is some space on repos' servers it would be better to keep the one previous version of each package at least through one week, and after this time delete it only if no one submitted any bug related to newest version (it isn't mask). This would allow users to downgrade broken packages even if they haven't the proper one on their disk. It may be realised using cron, adding cron task automatically when adding package and deleting the task while repo maintainer masks package.

Pacman already supports very simple package masking (IgnorePkg), but it doesn't let to specify version of masked package and repo's maintainers cannot use it to block packages globally, so it's inefficient.