This is very interesting. I've had my 5DMkIII since March. The first time I used it, I shot RAW + jpeg as I was only able to use the jpegs because I was travelling abroad and also didn't have any RAW conversion software with me that was capable of converting the RAW files. The in camera jpegs showed a few seemingly randomly placed black dots surrounded by lighter pixels - they looked a little like 'X' marks the spot! I'd never seen anything like it on my 1DMkII. They were quite noticeable at 1:1. When I returned to the UK, I upgraded from LR3 to LR4 and developed the RAW files in LR4. I haven't noticed the dots in any of the converted files, not that I've looked very hard but there's nothing that immediately stands out. As the in-camera jpegs are too mushy due to overly aggressive noise reduction (even with noise reduction turned off in camera), since I came back to the UK I've only shot RAW and converted with LR4. I've been reasonably happy*** with IQ and haven't noticed any hot pixels/dead pixels at all - not that I've been actively looking for them. When doing beauty retouching I often work at 1:1 or even up to 4:1 on occasion, so I'd have thought I would have noticed any hot pixels if they were there. To be honest, I'm not going to go looking because even if there are a few hot pixels/dead pixels they obviously aren't affecting overall IQ without a lot of pixel peeping (even with). I am intrigued to know though what my particular type of hot/dead pixel is/was - can anyone enlighten me? Until reading this thread, I'd assumed they were some sort of artefact produced by the in-camera jpeg conversion, particularly as I haven't noticed any (yet) in the RAW files.
*** I don't want to go off topic, but I say only 'reasonably happy' because IQ from RAW files converted with LR4 are quite good but the RAW files are noisier than I'd like even at low ISO (400 or less) and need quite heavy NR settings in LR4 (e.g. up to luminosity 70, detail 60) which results in loss of some fine detail. Also, although I don't use in-camera jpegs it would be nice to be able to do so e.g. for client proofing. I'm of the mind that this is not quite good enough for a camera at this level and I'm hoping for a firmware update that will improve the in-camera NR. I'm also hoping for a LR4 update as although I like the results, it is very sluggish when doing local adjustments.