Anyway, I was able to record 25 minutes thanks to the latest 1.00A firmware, but stopped after the sensor went to 54 deg C.
I've been doing a little research into sensor temperature. What I've found is mostly about what happens to the signal-to-noise ratio as the temperature goes up (i.e. it gets worse). If someone has a source of a spec sheet for a typical camera sensor (CCD or CMOS) I would be very interested to see what the maximum listed ambient temperature is. And even that probably just tells us the max temp that the sensor will perform to spec - not the temperature at which sensor failure might occur.
Also, do we know where the sensor temperature comes from ? If its build-in to the sensor then it will read much higher than ambient.
Just for fun, I ran a one hour video at low resolution and found that the temperature rise of the sensor (as reported by CHDK) was the same as it is for HD video. So it seems Canon was not concerned about temperature exclusively when they set the 10 minute limit. Especially as they could easily monitor sensor temperature and shut down when it gets too high. In fact, they may very well already do just that.
However, a "hot" sensor might be just fine for the sensor but dangerous to components around it. P&S camera manufacturers pack a lot of stuff in a very small space for an amazingly low price. Its not hard to see things shifting a bit at temperature extremes. I actually found a Canon service notice that suggested this was happening with some older cameras :
http://canoncanada.custhelp.com/app/answers/detail/a_id/4304/~/service-notice%3A-ccd-image-sensor-advisoryhttp://www.imaging-resource.com/badccds.html#cause - read the detailed description of the malfunction.
Will appreciate it if you will provide a PS.FI2 file, so I can test it with my other 32GB SD card.
A ps.fi2 file will get released when this update goes into the autobuild. However, you don't need it as you can format your 32G card with a single FAT32 partition for autobooting. Just follow the instructions given here :
http://chdk.wikia.com/wiki/Prepare_your_SD_card#For_Cameras_Released_After_2010_: