I've yet to see something smaller than a Glock 26 or XD-9 SC that I would trust 100%.
My dad got a Taurus Millennium Pro a month ago. The thing fired with the safety on. After Taurus "fixed" it, it still fired with the safety on. Well, this time you had to pull the trigger twice for it to fire -- the first pull jiggled the safety, then the second pull fired.
I see a lot of people who like Kahrs, but I've heard several times that those things just aren't made to put a lot of rounds through. Never really heard anything bad about them other than having to replace the springs a lot. Maybe that's untrue, but they aren't really much smaller than a Glock/XD, and the Kahr's are always about $100 or $150 more.
I really like the size of the Kel-Tecs, but I'm honestly surprised to see how many people carry them given the amount of bad stuff I hear about them. From the looks of things, more than half the people with a Kel-Tec have extraction problems. It's scary how many people I see talking about this "fluff & buff," picking the right ammo, and going through a huge break-in to try and make a Kel-Tec reliable. It sounds like you need about 2,000 rounds through them to break them in, and they start to wear out after more like 200 rounds. Nice that they have a good warranty, but I wouldn't trust one.
I also really want to like the Walther PPS, but the only review I've seen of the thing (well, the only review that wasn't a golden sample delivered by Smith & Wesson) was from a guy who had his PPS break after 20 rounds, then when he sent it back they scratched it all up when they fixed it.
In the end I've decided that I'm probably better off sticking with my Glock 26 because it's actually comfortable to shoot and I can get a lot of practice with it, even if it is a tad on the fat side. A thinner gun is going to be more concealable, but it's also going to bite into your palm a lot more, and I think people vastly overstate the difference between a 30mm wide Glock and a 26mm wide PF-11 and a 22mm wide PF-9. I know plenty people who actually love the feel of their Glock 26 or their XD-9 SC, whichever one they happen to prefer, and I've never met someone who actually enjoyed shooting something smaller and got a lot of range time with it.
If I ever do go with a smaller carry piece, I'm pretty sure I would want it to be something lighter -- not necessarily something smaller. I'd probably get a 12oz Smith 360 and shoot light .38 Specials in it.