personally, I love my PE's. They've been my primary skis for the past 2 seasons and have seen the snow probably at least 150 days. I have had no durability issues at all, and I have pushed the hell out of my PE's. They have seen ice, bumps, groomers, pow, rocks (unfortunately, good thing I enjoy tuning), air, some rails, some boxes and no major issues. I've never heard anyone complain about the PE's (in person) and the most common gripe I've heard on the net is about weight (as a park ski they are a little heavy, but nothing unmanagable). I'd recomend them to anyone, and have referred to them as the best bang for the buck ski I've ever had.
Yuki, you commented about older Merlins and gettign stress cracks leading to delam, normally this is primarily caused by landing on the tails, causing the tips to snap down to the snow, which is bad form in the air, not poor construction/quality. However, you mentioned they were used "pushing level 1" classes, so I'm guessing these skis got run over a "few" times as well, students have done more damage to my skis over the years than I have, so that might have exaserbated the problem.