Ahh, it was related to your post...
I'm a pyro. Accuracy is not an issue.
Yeah, but as previously mentioned, the pyro is an incredibly underpowered class, and shouldn't be played by anyone.
This is quite false. A pyro who's in the right position at the right time can cause extreme damage and confusion. Not only does his flame (especially if 'twirled') draw attention, the airblast can be used to buy enough time for an escape. If you live, which most decent pyros do, you've not only taken half or more of everyone's HP but you've also broken the line.
Think of pyros as molten war dogs. You unleash them at the correct time in the correct place and you've got a screaming, flaming, confused group of enemies who are desperately trying to find water, a med-pack, or the pyro. That's all it takes sometimes. This is only one of the uses of the pyro. Granted he's not good for EVERY situation, but that's why knowing multiple classes is a good thing!
And as far as the "no aim required" argumenet goes, I've found that using the flamethrower effectively DOES require a bit of aiming focus. Example:
You run into an enemy crowd consisting of 1 resting demoman, 1 medic, 1 engineer, 1 soldier, and 1 dispenser.
The wrong way- You wildly spurt fire everywhere in hopes that you'll get a kill or two before exploding. The soldier blows you up immediately.
The right way- You quickly mark each player in your mind with a kill priority. Soldier first, demo at the same time if possible, then the medic and engineer. Lastly the dispenser.
Now that you have an actual game plan, you'll need to execute it smoothly. Taking out the soldier and demo quickly is a must and therefore you'll need to focus ALL of your damage on them before the confusion wears off. Getting a feel for the thrower will allow you to arc your flame while you strafe, causing every bit of the fire to hit the enemy. Strafe, jump, duck, all while pouring napalm on your targets. When the two are down, do a quick twirl to ignite everyone else and begin working on your next targets.
You could also simply set them on fire and hide while your heavy/medic friends jump from behind a corner. Flaming fish in a barrel! As a bonus you can sneak back up and roast them while they attempt to take out your pals.
Damage output from the flamethrower all depends on where it's aimed, how long it's aimed, and if the flame even hits. You'll notice that with 1 on 1 pyro battles your flame will often 'derail'. These moments are wonderful fire arcing practice. If you can keep your flame on the enemy pyro the ENTIRE time he's strafing and carrying on then you know you're ready for a large scale surprise attack. It does take skill to pull one of those off.. and a bit of luck, of course.