When I search my Channel by the name of a tag (like "work") I get no results, even though I know I have at least one video with that tag.
See screen shot:
Also, if I try to create a new section on my YouTube channel page, it doesn't show me my news tag ("kids!") as one of the Tag options (for add section content by Tag name).
Tags (and, for that matter, HTML <meta name=keywords>) don't really get looked at by search at all, neither on YouTube nor on Google and most other search engines. They do get used for related videos though, and YouTube from time to time experiments on making them more useful (like the "tag sections" you mentioned that since have been removed again), but as of now, videos only containing the search term as tag don't show up in search.
