Hi - I just installed SEO Title Tag on two blogs, both 3.0.1. It worked first time on the first blog but not the second. After some poking around, I noticed that it appears to conflict with another plugin, the All In One SEO Pack. Once I deactivated the All In One SEO, the SEO Title Tag plugin worked perfectly.
If you are having issues with SEO Title Tag and have the other plugin installed, try deactivating the ALl In One SEO Pack and see if that helps you.