Especially with the Open Graph module (which I've had to disable until I can find a way to fix this / a patch is released), this plugin spits out multiple "Notice: Undefined index" errors that make their way to the page's HTML.
With these errors not being caught before output, they are wreaking havoc on page layout. They are not staying in the
<head> area, but (as they are untagged text) are bumping down into the top of the
<body>, along with all following meta tags. This effectively negates all meta-related SEO.
The specific error I've come across last is: "Notice: Undefined index: twitter in /***wordpress/wp-content/plugins/seo-ultimate/modules/opengraph/opengraph.php on line 211".
This shows up twice; before twitter:card and before twitter:site meta tags, which are bumped into the
<body> by this error text.
Googling "undefined index"+"/wp-content/plugins/seo-ultimate/modules/" will show a fair few people with this problem, active, relating to a number of different code lines and modules.