Before 5.2 they definitely were not too good. It was difficult to burst someone down quick enough in world PvP without either A) them fighting back and you having to run, or B) you couldn't kill them fast enough before people around them would notice and come help.
I've been playing my frost DK and world PvPing with him, and while it's good to gank someone and pop CDs and burst them down to no health, it's also a bit annoying not being able to pick and choose my fights like I used to do with my rogue.
So are rogues back on top for world PvP/1v1s?