Guys, I don't want to start another complain thread on it (there are a few already). Rather, I want to share my experience after fw1.03. I sort of agree with many others (Smeggypants) claiming that the fw1.03 is somehow inconsistent in low light conditions: sometimes it works and sometimes not. I have the feeling (though nothing scientific here) that my previous body (k20d) in the same conditions would probably refuse focusing. In other words, perhaps the autofocus issue is there just because the new safox is much more sensitive in low light, and thus more prone to errors.
Nevertheless, I recently bought a split image, microprism collar focusing screen (I won't tell the brand, I'm not related anyhow with it!), and I can say that it helps getting rid of that 10-20% of missed low-light focuses, especially thanks to the clever Pentax quick-shift manual focus.
As a proof, I attach here a shot I took some days ago: as you can imagine, it was a steal, quick shot, no too much time for adjusting parameters. Low light, mainly tungsten light, focus on guy's face and recompose, with the face shifted within the microprism collar. I quickly noticed the wrong focus and adjusted it manually. The result is pretty good, in terms of focus. And taking shots is even more fun!
In conclusion, I actually feel this focussing screen such a great addition to the camera, that I wonder why Pentax is not installing it by default on every camera, especially in the semi-pro level like the k-5. I think that this is one of the things "I REALLY want" from future Pentax cameras.