When I needed a thin conceal carry gun in 9mm, I opted for the Taurus PT709 Slim and I love it! (see review here) It shoots well, never jams or fails to feed through hundreds and hundreds of cheap practice rounds and has eaten a box of expensive 9mm Hornady Critical Defense and a box of Federal Hydra-Shok Personal Defense Ammo without a single problem. I've even ordered a Crimson Trace Laserguard for it (hasn't arrived yet)!
While I can handle a .380ACP or .25ACP with one finger on the trigger, two on the grip and a pinky dangling free, the recoil of +P defense ammo makes it hard to keep the pistol from squirming around in my hand. To get all three fingers on the grip I ordered Pearce Grip Extensions for the magazines. I instantly liked them but worried that they would compromise the purpose of a short grip pistol, concealability. A quick test in my Crossbreed IWB holster revealed that there is virtually no difference in the ability to conceal the PT709 Slim with the Pearce Extensions installed. It does make it tighter in baggy cargo pant pockets but in a holster, no difference.
The Pearce Extensions are well made and fit perfectly in the notch at the bottom of the grip. I'm really glad I bough them and would recommend them to anyone that has a compact conceal carry gun that wants to cure dangling pinky syndrome. Even though I said I could handle my Taurus 738 TCP with two fingers on the grip, now that I've used the extensions on the Slim, I'd like to see Pearce make them for the little TCP.
UPDATE: August 28, 2012
Pearce now makes a pinky extension for the Taurus 738 TCP (see review here). Note that if you have a TCP with a serial number that ends with a "C", the extension will need minor filing to fit properly.