It's actually a little different from that if I may.
First, my perspective is only that of an enchanters, but here's how ours work: All standard charms (there are two exceptions i'll get to later) are randomized durations which can max out at 8 minutes depending on a combination of your luck and your charisma. As a high end enchanter after debuffing the MR of a mob, and with me at max CHA, i get near-8 minute charms pretty much every time. Also, the charm spells themselves are an incredible debuff. If you were to take 2 mobs of the exact same level, charm one, and send it against the other without interfering in any other way, the other mob MIGHT get to 70% before your pet dies. If you are going to charm for anything except crowd-control you need to haste your pet, slow the mob you are attacking, use stun if you can, and nuke nuke nuke / pray. Kiting also works well if you have good run speed. What else... oh right, in continuing with the huge debuff that charm itself is, there is an issue with hastes. Charm either (Wiz needs to clarify this i think) makes the mob only hastable to 50% or only gives 50% of the haste bonus you cast. It's also removes any of their abilities the mob might have like frenzy, rampage, extra attacks, etc. Pets are not fully healed when charm breaks, however there mana is fully replaced. Of the 3 enchanter is the best of the best. You will really only ever find enchanters charming in 90% of all situations. Necromancers may charm a little in freeport and some druids/shamans(???) might kite with an animal.
As far as how effective charm is overall, it's a tough call. I charm in most groups that i'm in unless we are fighting undead (yes enchanters can charm these) and only then because undead mobs cannot be stunned, so a break in a fight with a hasted mob that now has it's debuff removed and attacks me and my group is bad. Otherwise I have very few problems controlling a standard charm pet. I believe, but am too lazy to check on the spell parser, that the 2nd and 1st highest level enchanter charms also have a POSITIVE resist adjust, meaning they are harder to land on mobs. Tash tash tash

syduck: