One of the most interesting widget on WP is the Tag Cloud thing. The more posts you write with a tag, the bigger that tag becomes, so readers can quickly identify what type of posts you have written the most, and what type of posts you just wrote a few times about.
But I don’t see some of the new tags that I put down for my last post. I tried dropping the tag cloud widget and adding it back in, but the tags were still missing.
Now I’m writing this non-sense post to test this hypothesis: the tags for the newest post do not show up in the tag cloud.
… And that hypothesis is disproved, because those tags still did not show up. So I would conclude that tags in the tag cloud appear whenever they feel like it. (a time lag, probably?)