I used Preatorians a lot in 5th and they were quite difficult. But with new jump pack rules, and the change to their close combat weapons, I am now trying a 5 man unit with a destroyer lord.
It's my only close combat unit in my list.... I haven't tried it yet though, but it's the only way I see them working in 6e. Not that it's a bad thing, but the Lord should help with his Preferred Enemy.