Another thing about tags is that I feel they should either denote something uniquely identifying about the thread they're applied to, or not be used at all. Take this one for instance:
With one exception, all of these tags are better covered by a search. Say you're looking for a plugin with some kind of YouTube functionality. Sure you can get a decent overview with the
youtube tag, but you won't trust that to be an exhaustive list, because you can't trust people to have tagged their threads appropriately (a common issue for WordPress plugins for instance). So you search.
As soon as you go past 1-2 tags it's also very noisy (especially in combination with the Topic Badges, which I'll make a separate comment on)
The only tag I find worthwhile is
imgshow, and that's assuming it would be unique to this plugin. This is where hierarchical tags (think Google Code issue tracker) can be very useful, because you could make rules for special tag groups, e.g.:
If I create the first instance of the
plugin:imgshow tag, I am now the owner of this tag. I will get a notification of all new threads using this tag, and I will have moderation rights over every thread that uses this tag.