I stand by my previous opinion: distribution tags are for the most part not warranted. Since a program that runs on Linux will run on any distribution, using a tag like debian to say “I want a program that runs on Debian” is a misuse of the tagging system: a question asking about a program to run on Fedora would have exactly the same answers, thus the question should not be tagged debian, it should only be tagged linux.
The tag debian should be indicative of a question that's specific to Debian, for example software designed to interoperate with Debian's build infrastructure or their package distribution infrastructure. This is an extremely specialized requirement that I don't expect to come up for a long time yet.
The tag ubuntu is a bit of an exception… because it isn't really supposed to mean “I want a program that runs on Ubuntu”, but “I want a program that's integrated in Ubuntu”, which is a stronger requirement. However the nuance is so subtle that I don't think it's realistic to expect everyone who chooses tags here to be aware of it, let alone understand it. In fact, in practice, the requirement tends to be integration with Unity, not integration with Ubuntu, so the right tag would be unity — but most people who would use this tag are not aware of the distinction and might not even be able to name Unity.
The distribution tags are causing more harm than good because they needlessly fragment the taxonomy. If I'm looking for a program to run on Linux, it might be on a question tagged linux, or tagged ubuntu, or tagged debian, etc. Imposing a rule like “all questions tagged ubuntu must also have linux” is not an option: the rule wouldn't be followed, it takes up space in the 5-tag-per-question limit, and it conflicts with the desirable use of ubuntu as actually meaning something (because questions that are really specific to Ubuntu should not be tagged linux).
Given that distribution tags are consistently misused, I propose to merge all existing tags for Linux distributions into linux, and delete them all except ubuntu which we'll keep as a synonym because it gets used so often.