Personally I've not found the Z11's particularly delicate in use as long as you realise that these are plastic notebooks and don't take the 'carbon fiber' to mean 'indestructible', and the build quality is decent - back to form for Sony after an indifferent '08-09. Also, a dose of common sense (sadly lacking on many people I see) wouldn't hurt - you can see that the screen is whippy. So don't put effin' books on it all the time then complain that the keyboard is marking the screen later.
The lighter build does certainly make it seem more insubstantial, but I've (well - for the most part it's other idiots who drop it for me, e.g. by forcibly pulling their bag out of the overhead and dragging my bag with it, etc) dropped enough previous-generation 'carbon fiber' machines to know that they survive better than many apparently more solidly-built machines. In terms of actual durability / surviveability, I'd rate the plastic Sony's pretty high - certainly way over more obvious-metal machines.
I have extremely rapid refresh cycles combined with a 'buy-em-all-and-personally-see-which-is-best' approach, and I'd have to say the Z11's are easily my best mainstream, actually portable, notebooks to date in terms of overall utility.
