I didn't encounter any problems with aggro until my 60's (I used boars through 67 or so). If I had to level to 70 again, I would add a bird with screech around lvl 40 then switch to all birds at 61 or so (the ugly, 2-headed things from HFP). Outland dungeons are much tougher without Screech and my biggest frustration while leveling was grabbing aggro with the priest before I had all my "toys" like PoM.

The firing squad formation is quite effective (and looks pretty cool) but gimps dps if you ever pull the mob off the pet. Frost trap helps for that as well. Essentially, I found that for PvE, the slight dps/synergy hit you take is more than made up for by the fact that you rarely have to melee or trap anything that peels off on your team. Keeping everything range is a huge advantage all the way around.

That said, you can pretty much do anything you want from 1-55 and still be a well-oiled killing machine =)