Auto complete doesn’t work. I would never notice, though, I simply choose the tags from the various services like Yahoo and Zemanta, etc.
I stand corrected. But it’s something I don’t use anyway, which is why I didn’t notice.
On another site, unrelated, I do have auto-complete tags, and I’m not sure if it’s through SEO Ultimate plugin or not, or through Efficient Related Posts. I’ve checked documentation on both plugins and neither claim to auto-complete tags, and I run the same theme on both that site and the one where Simple Tags is installed, so it’s not a theme issue.
The site where the auto-complete doesn’t work also employs SEO Ultimate, but it’s brand-new still.