This provides some details :
http://thehackernews.com/2015/02/hard-drive-firmware-hacking...
So no, they'll get a rootkit process running on your machine and (for instance) upload everything on your hard drive through your web browser.
Another thing they've done is to upload hacked drivers to cause other hardware connected to the infected machine to physically destroy itself.
There's also that this particular kind of compromise is basically inapplicable to hardware. What are they going to do, put a 3G radio in your laptop that broadcasts your "data" via the cell network to Belarus?