I am personally not a fan of text changing/appearing/disappearing on mouseover as happens now quite a lot in the forum list and thread list pages. I find it distracting and a bit annoying.
I don't find it that irritating, but I guess that's a question of personal taste. It's certainly one way to display a lot of forum-related info without cluttering the index page.
For me, sometimes the row size (or something) changes, so that the whole page jumps up and down slightly as I move the mouse over page elements. I would think that's probably not intentional....