The LeTech is a triple pivot unit with a really long cage- the Disraeli Gears site mentions them being "fragile." I can just imagine somehow catching that cage and it having the leverage to tweak any of those pivot joints...

I have a LeTech- I've been in the process of redoing the bike that it lives on for about the past year or so... There are many other derailleurs I would prefer to use before the LeTech.