When you directly post a blog entry without scheduling, then WordPress.com adds this to your URL: &message=6&postpost=v2
It alters the left pane indicating how many posts you have done so far, but more importantly: suggests some tags based on the content of your post.
You can add this pane yourself by adding &postpost=v2 to your post editing URL.
So if your URL is something like this:
and you make it like this:
then you can add the suggested tags with ease.
I find that much easier than to use the “Choose from the most used tags” feature.
–jeroen
