Hard drives have gone down in reliability over the past decade because drive manufacturers are having to get more aggressive in the designs to keep increasing the storage densities.  In the 70's and 80's read/write heads rode on a cushion of air just above the disk.  Then in the 90's drive manufacturers needed to get the heads even closer to the media so they put ripples in the disk surface and allowed the ultra-light-weight heads to "skim" along the disk as they rode up and down in a sine-wave pattern (you can't allow the heads to touch the surface of the disk if both are really flat because both surfaces are now so finely made they're too "smooth", and "stiction" will cause the two surfaces to bond to each other.   The thickness of platters and heads are being pushed to new lows, requiring different materials to be used such as glass just to prevent wobble or surface deformation in the platters.  And they're also pushing the rotational speeds up.

So... hard drives are becoming much less expensive per byte, but more fragile in general.  It's the nature of the beast.

What would the failure rate of the PS3 hard drives be?  Who knows.  It depends on the hard drive Sony uses and how the hard drive is used.  The company I work for supports 5000+ enterprise desktops, and on more than one occasion we've had to just go through and replace large lots of hard drives because that particular model from that particular manufacturer is experiencing large numbers of failures.  We also see a lot of hard drives die prematurely due to too much "thrashing" depending on usage patterns, i.e. - the read-write heads are forced to constantly seek back and forth across the disk at high speeds.   Sony seems to have put high-quality components in the PS3, but I doubt they'll perform better than other high-quality components in the industry.

I'm not trying to start a troll wars, I'm just asking a question.

On the PS3 official french community forum ( http://community.eu.playstation.com/showthread.php?t=156146&page=34 ), more and more ppl are complaining about the PS3 lens problem. Apparently, the console sometimes crash (mainly with PES but other games too) and once reboot, the console itself still works, and you can play demos, use PSN and such, but it doesn't read BR discs anymore. At all.

 Is it a "local" problem or does it happens in your country too ? Any idea of how big is this problem ?

I don't have a number and I don't have a source ... Just having heard "less than 1%" is not very trustworthy, or believeable. Also, less than 1% is not (in general) believeable because (unless Sony found 'magical' hard-drives) the hard-drive's failure rate shoud be noticeably higher than that.