Actually, this differs from our group's experience with Dirty Trick a great deal.
Any maneuver can ruin a DM's plan in a heart beat. One of the players accidently disarmed a monster, causing its death (Heros system but the same could happen in PF)
At the VERY least, you're denying a full attack against monsters that have multiple strikes. A bear that has to clear it's eyes is only going to get a single swipe against your character, rather than claw-claw-bite. The same is true of human opponents with iterative attacks.
Or, say you blinded a bear and it just full attacks you anyway, it still has a +13 to hit with 3 attacks, sure the rouge may kill it on their action but all that is protecting you is a 50% miss chance, odds are, at least 1 attack is gonna hit, possibly 2. Even if you did a shaken it is only a -2 to hit
On top of that, once you get 6 BAB, you can pick up the "Greater Dirty Trick" feat for an additional bonus, longer duration, and a STANDARD action to clear the condition. At that point, you're denying a round's worth of actions as a trade for your attack. Kicking a dragon in a sensitive spot and denying him everything but a move? Priceless.
Too bad it is level 7 to get it for all but the fighter. And most. like the rouge, have to wait till level 11 to get it.
It is also not just 1 attack, it is all your attacks that round (2-4 of them)
P.S. Go ahead and kick a dragon in a sensitive spot, you will be food as they pretty much ignore the penalty till it is over
I'm not saying it's perfect, but we've got a defensive fighter in my current party who frequently uses Dirty Trick (and has the feat chain) and it has proven invaluable against bigger foes. It's not the solution to every fight -- when it's lots of little guys, just hit them -- but our fighter has turned the tide multiple times when the party was on the ropes. It's really beginning to get on the DM's nerves, since most of our battles end up looking like the Three Stooges are in town, but it's undeniably effective.
Not to mention that the dual-wielding rogue who flanks with the fighter just loves it when he blinds them... Sneak Attack goodness.
I am going to assume you are about EPL 7, maybe 6. Your DM needs to learn to diversify what you fight. Blind does nothing against a foe with blind sight or blind fight feat, entangle is pointless vs non humanoids (no pants to pull down) deafened is only good vs casters, shaken does not affect fearless creatures, nor does sickened affect constructs or undead. The only one consistently useful is Dazzled
While I can see it being useful, Dirty trick is simply not worth the 3 feats to get it to work consistently where as others can be with just 2 (the third feat being icing)