how big a deal is uncanny dodge?

[CyberThread]

Just overall, in day to day of an adventure, how big of a deal is uncanny dodge?

[Flickerdart]

Not that big a deal. It mostly matters if the DM uses a lot of creatures with SA, but there really aren't very many of those around.

[Novawurmson]

Much bigger deal to lightly armored classes than to heavily armored classes/monsters that rely purely on natural armor.

For example, consider three creatures with AC 18: One with a chain shirt and Dex 18, one with a breastplate and Dex 14, and one with +8 natural armor.

For creature #1, uncanny dodge can be a +4 to AC when they would be flat-footed - quite likely to be the difference between a hit and a miss. For #2, it's a +2 - important, but not critical. For #3, it's completely worthless.

As for how frequently it will come up, it depends mostly on your DM's playstyle. If your DM just throws single monsters at you, it will very rarely come up (in the surprise round and for invisible monsters), but your party will probably wreck everything anyway because "lol action economy." As a DM, I've recently fallen in love with 4+ opponents per combat, so it would help you a lot in my campaign :P

[Emperor Tippy]

Considering that you can get Improved Uncanny Dodge permanently for the cost of an ML 11 powerstone of Danger Sense and an ML 13 powerstone of Incarnate, it's not worth wasting levels on.

[Shining Wrath]

It matters if you rely on Dex as a big part of your AC *and* you get ambushed a lot.

Improved UD, as gotten by Barbarians and Warblades, is a bit better because you can't be flanked. Very nice for big brawlers with D12 HD who find themselves in the middle of a mob often.

[eggynack]

Considering that you can get Improved Uncanny Dodge permanently for the cost of an ML 11 powerstone of Danger Sense and an ML 13 powerstone of Incarnate, it's not worth wasting levels on.
On a similar note, you can also pick up uncanny dodge (though not the improved version, at least by this method) by getting eternal wands of primal hunter and instinct, and using both of them on a daily basis. That's 15,320 GP, and you also get a +5 competence bonus on initiative checks, and can do the same to another person. It's a method that seems to have some advantages and disadvantages compared to your method, so it's a plan worth taking note of.

[Person_Man]

It's equivalent to one Feat - Shape Soulmeld (Impulse Boots).

From a metagame perspective, it is a highly situational ability.

If you have high Dexterity, it's likely that you're going to win Initiative against most enemies, and it's probably unlikely that you'll be Surprised very often (since most high Dex builds also have Spot/Listen), and thus your Uncanny Dodge is mostly pointless. Conversely, if you have low Dexterity, there's not much difference between your normal AC and your AC + Dex, so Uncanny Dodge doesn't really get you very much.

The situation in which it is useful is when you are being attacked by Invisible enemies. In that case, it can be very useful. But how often that actually happens in a game is highly dependent on the DM.

I personally would never take a level of a class or make the Feat investment specifically to get it. Though it is better then most other "filler" abilities (Trap Sense, Still Mind, Endurance, etc).

FYI - you can also pick up Immunity to Flanking for one Feat - Shape Soulmeld (Threefold Mask of the Chimera) or Exotic Weapon Proficiency (Longstaff). Either is strictly superior to Improved Uncanny Dodge, which has the Rogue level exception. (Though you have to fight defensively or use Combat Expertise while using the Longstaff to gain it's Flanking immunity).