Allow your mouse to hover in between the thread title and the star and a cog image will appear. Right click where it says options and then select dismiss.
Bam it goes away. (Saw the instructions on another board and I was so pleased. I really am not a fan of the new layout - it's too white and it lacks the organization I like from the other version, but hey...maybe I'll get used to it.)
Re: Dismissing announcements at top of forum
ETA: Actually now for me if you just click the cog it gives you the option to dismiss and no right clicking is needed.
I wasn't seeing any stars or cogs, they don't appear unless you are logged in. Just wanted to share that for anyone else who is having trouble.