When I am on my druid, I do not like getting near ret paladins. I save my PvP trinket purely for a Hammer of Justice, getting caught by a ret paladin's stun is usually never good since a good player will know to never roam around alone(meaning there will most likely be another person slapping me around while I am stunned along with the ret paladin).
Last night I saw this warlock putting DoTs on me. While in my FC gear, I was able to outheal his DoTs with rejuvenation. Nuff said(thought he could of been poorly geared)
Was fighting a Crit-Arcane Mage in a duel on my druid's healing gear. They have very decent, arguablly one of the strongest burst damage. I haven't seen any decent geared mages use frost spec yet, mostly people sitting at 800 health so i just /ignore them. I would think that Early frost and improved cone of cold talents would serve as a really nice CC with the combination of a water elemental. And frost mages might not have nice burst damage as an arcane mage but they can actually do 'okay' damage but moreso CC. And since paladins no longer have HoF, the only real classes that give frost mages problems with CC'ing are shamans and druids but shamans are so unplayed now adays that druids are the only ones that give a CC mage problems.
Summary: Ret Paladins are viable. Warlocks 'might' suck now but that's based on experience fighting a random one in wsg. Arcane mages are definately good if played correctly, unsure about frost mages' DPS but definately could do some good CC if played correctly.