I just recently bought a C.T.A.C. from Comp-Tac for a Sig. See here:
C.T.A.C. I haven't really run it through its paces yet, but initial observations are positive.
Here are some of my random thoughts about it Kydex vs. leather. Subjectively, leather has a better feel and I slightly prefer the "break" from a leather holster to that from Kydex, although a Kydex holster has a more crisp break. Both are capable of securely holding a gun. Kydex doesn't soak up sweat in the summertime. Kydex is generally cheaper for similar quality. In general, Kydex makes a suitable alternative to leather, but leather is "nicer".
To answer your question more directly, I haven't spent much time with polymer pistols and Kydex, but have handled a few in cheaper Kydex (Fobus) during range sessions. They seemed to work well and retain the guns (Glocks and XDs) fairly well. I don't know how well they would work for daily carry, but I would sure prefer a Fobus to the nylon holsters.