Dpreview liked it's image quality but apparently had problems which seem to me to be quality control issues.
Let's talk about the positives first; the Pentax smc DA* 55mm F1.4 SDM is undoubtedly a lens capable of producing wonderful images, with a blend of optical characteristics near-perfectly suited to its intended purpose as a portrait lens... Unfortunately, though, we have serious concerns over two issues with this lens which have to temper our enthusiasm; namely optical alignment and autofocus (which are quite likely related). Over the course of what has become a rather protracted regime of testing, we've looked at three samples of this lens; each has shown a clear tilt to the focus plane, most pronounced in the first sample, and least problematic in the last (which we finally decided to use for the published tests). This does more than simply mess up our studio tests - it clearly results in real-world image quality and focusing problems too. In fact we've never before seen a lens so capricious when it comes to focusing - we're used to F1.4 primes being challenging for cameras' AF systems, but the 55mm was most difficult of all.