If something better came along that helped us rather than slowed us down it would be fantastic.
JIRA is absolutely terrible as well. I can't express in words how much I hate and dislike JIRA, it's horribly slow and bloated user interface and how complicated it makes certain tasks... using it as an Agile tool makes it even worse especially with Greenhopper the add-on.
Confluence is very stable. We have a ton of content in it, and without it we are completely dead in the water. It works well.
Yeah the tags are a bit ambiguous, but I have never seen the tags get in the way. Downtime would get in the way much more.
Having used Bugzilla, Trac, Mantis, MediaWiki, and several other tools I 100% prefer Jira and Confluence...
I tend to use Trac most.
(Mantis might have less capabilities than Jira, but I almost enjoyed working with it. That might have depended on the project. [Edit: On consideration, Mantis was simpler and didn't make me scream from pure hatred.])
On the plus side, you can charge them lots of money. On the negative side, it's not as easy (or cheap!) to market to these people and take care of their needs.