Well, I'm playing a cleric currently. I'm not turning focused, just a full-level cleric (for turning, anyway) with a 16 Charisma.
So far, I've used it ... three times? Over the course of 14 levels. The first time, at 5th level, it worked pretty well. The second time at 10th level it worked great, against what WoW people would call "trash mobs" ... a throw-away encounter against much weaker foes ... recently, I rolled a the top result and almost max HD (1 off) and turned ... 1 of 5 foes.
Turn Undead is pretty powerful, because it's a check that can cause an enemy to flee without a save. To counter this, they give pretty much anything but mindless shambler undead at least +4 Turn Resistance. Additionally, beyond early-level skeletons and zombies, you get into the low-CR/high-HD zombies and skeletons of large and larger creatures ... for instance, a CR 4 zombie has at least 12HD, meaning a cleric of 8th level needs to roll a 22+ turning check just to be able to affect it.
Personally, it's more of an annoyance than anything else. If you can turn the undead you're facing, it's pretty much given that they're already so weak that you could blow through them without noticable resource depletion anyway. Even if it's given that you CAN turn the undead, then you have to go chasing them down through the dungeon as they flee all over the place, which at character-scale in rounds can take all ... friggin' ... night. Far longer, say, than just standing there and cutting them down. If you can smoke them with your turn check, then, really, the only reason the undead were there in the first place was to make the Cleric feel good about his Turn Undead ability ... they weren't an actual fight, just an excuse to use Turn Undead.
Personally, I get more use out of Divine feats that burn Turn attempts for other things, and I'm undead-slaying focused. It's just not worth the trouble to go chasing the buggers through the halls even if the turn DOES work and, if it's undead of any real threat, it's probably not going to work.
--fje