I use it for a few of my sites. The problem with Joomla for "SEO" is that you really don't have as many options as you have for wordpress.

Wordpress has lots of search engine friendly plug-ins. Joomla has a lot of user-friendly plug-ins.

If you're starting a membership site or something very technical and complicated, then joomla is the way to go.
If you're trying to rank on the first page of Google then go with Wordpress because its much easier to do so.

Cheers!