Well it seems people lost an interest in this thread some time back, but I thought I'd post a little something. I believe strongly that most companies DO employ some form of planned obsolescence. In the vpl-hs51's case, the ventilation is COMPLETELY inadequate.
Stock settings, you can make out 'heat waves' (much like looking at asphault on a very hot day) when you are very close to the screen after only 1.5 hours! This is very subtle, and not really noticeable at all unless you are right up to the screen, which, by nature most people wouldn't notice. With high altitude setting on, this increases to about 2-3 hours before onset, but going more than that DOES start to put heat wear on this model like you wouldn't believe.
An easy fix? Hot glue two regular computer muffin fans to the front grill and wire to a 12v AC adapter. For me, I can now run the projector, even on High lamp, without any 'shivering' or 'shakies' when looking up close. This should, in theory, prolong the life of the lamp and the projector a great deal. Scanning this thread there are reports of people who sent their pj in and had the fan upgraded and high altitude switched on. I firmly believe this was a known issue, and they did nothing about it. Also, if you are having issues with shakies and know its not heat, try putting something moderately heavy on top of the projector, like a portable jump starter or a speaker.
Anyway, I recently got this pj off ebay and am loving the hell out of it. Playing team fortress 2 on a 12 foot screen FTW.