this is part of the popular svbtle blog network theme and the obtvse theme copied from it. You'll see this theme used on at least 1/3 of the blogs posted on here, I've always been against the whole "mouseover-as-action" thing too.
There's also a new branch that looks very different: http://natewienert.com/
You might be thinking of WP-Svbtle which is closer to an exact copy.
Apologies for making an off-topic "correction" like this, but Nate Wienert seems like a nice guy so I hate to see his project unfairly accused.