I just tried to add a tag for "implementation-defined-behavior" on SO but I couldn't because of the 25 char limit. I had to resort to an abbreviation (implem.-defined-behavior), which is rather ugly and to some extent thwarts the purpose of tags, i.e. easy indexing.
Although I acknowledge that too long tag names could be unwieldy, sometimes there are technical terms that cannot be abbreviated in any useful way (especially when there is no widespread acronym).
Could an increase of that limit be considered?