The problem with the expanded popular list is that no matter how many tags you show, you still only show the more popular ones (unless you end up showing the whole list). What happens to the more obscure tags?
That being said, it's definitely a step in the right direction.
The search function sounds nice, but at the moment it would be nice if there was just a simple list of all tags on a page somewhere. Right now, the biggest problem I'm having on the site right now is that I have no idea what tags exist so I don't know where to look for content interesting to me, and I have no idea where to find what tags exist. Just give me a list and I'll CTRL+F like crazy, fancy stuff can come later.