None of them "work using a # and then the first word of the Category name". You can use either
#"Category Name" (in search, but not in text I think).
A "slug", if you don't know the term, in this context means the name as used in the URL.
The slug names for the categories have not changed. So #macro works because the slug for the "Macro Library" category is still "macro". #general works because the slug for "Questions & Suggestions" remains "general".
If you type
#ques, the forum software will popup amn overlay offering you the "Questions & Suggestions" category and will produce #general.
I'm not planning to change the slugs because a) it would break all existing URLs related to them, and b) they aren't that bad.
It would be nice if you could do #"Questions & Suggestions", but you can't - it works in searches I believe.