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Could we make tags imply other tags?
There are a number of tags, that imply other tags. Like if I tag my question django, then it implies python. Another example would be STL and C++. It would be nice for SO to add implicit tags when a question has less than 5 tags at the time of posting.
Additionally, if I ignore Tag A, then I automatically ignore all implicit subtags of A.
This won't work in practice because there are many times where the implicit tags wouldn't actually apply to the question.
For example, you could ask a question about the VB.NET language -- tag it with [vb.net], but [.net] should not be added because it's not relevant to the question.
How can you be sure that django implies python or stl implies c++? There may be other meanings in use that you don't know about.
Its likely to work for these two cases, but can't be solved in general. Even if it works out for some tags for now, who says it won't break later?
I think that's a bit redundant and would probably be less than trivial to implement, probably too much effort for the small benefit. If you have a question about django you'll probably search for [django] before [python].
My guess would be that most questions about software for a given language would also be tagged with that language. I feel it's better to leave this in the hands of the question's author rather than to try and guess at what tags should be added.
EDIT: I take that back, there's 7,195 questions tagged [django], and only 3,010 tagged [django]+[python]. But I still feel that these questions shouldn't be automatically tagged with [python], it seems like most are getting answered fairly well as is. If you want to ignore [python] questions it's easy enough to ignore [django] as well...
tag hierarchyproblem, since there is no hierarchy.