Probably it is different at higher levels - as I have only seen T1 content, I obviously cannot know how it works out later - but I've had a very decent success rate with the early PQs by (as Archmage) agreeing with somebody else that he tanks and I'll do the best to keep him alive (amazing what confidence that gives your tank) and (as Swordmaster) agreeing with somebody else that he heals me and exclusively me unless he has healing to spare while I'll do my best to keep the boss locked down. The early High Elf PQs seem to do very well with just one dedicated tank, one dedicated tank healer, and everybody else doing the <execute random order> chicken dance.
...It must be said that it is entirely likely that the success has more to do with the difficulty of early PQs - some are hard (the beach overrun with orcs and corsairs in Chacre has swamped every bunch of people I've tried it with in phase II) while others seem exceptionally easy - threemanned one in Chacre where we have to rescue prisoners with me as archmage (9) tanking the boss + healing myself, archmage (7) healing me, and a shadow warrior (10-11, I forget) doing the damage.
I have not really noticed people in guild chat actively recruiting others to perform PQs - is that because we are so spread in levels that the odds are low of gathering a decent group, a natural reluctance to inconvenience others, or because it has been an unsuccesful strategy so far? Or, perhaps, something completely different?