I had a Z10 for 2 weeks and it ended up driving me mad. I took it back and swapped it for an S3.
The build quality is fine, the screen very dark compared to an S3 or iPhone. Battery life was ok, probably around that of an iPhone 4S, but they are not that great. The S3 does much better.
The OS was ok. It had trouble deleting files, they would reappear. It would forget imap settings for different accounts, I think when a signal was interrupted, like going into basement carpark. Made it useless for emailing.
The actual hub is a great idea and well executed. Unfortunately a lot of apps don't open in each other, like in iOS and a little like Android. It throws you around a lot. Also a good few apps and some of those includes are essentially browser links to a mobile version of the website / app. The lack of apps was not really annoying, those included were almost capable.
But the bugs, there are many, you don't notice at first but after a while you can predict them. The most annoying is the screen dimming when its opening a new app, sometimes through the hub. But losing email settings, crashes and unresponsiveness, some silly implementations of straightforward ideas all add up to something that needed a few more months in development.
The worst thing however is the screen coating. Its not grease resistant meaning that after a days use the screen is really dirty and a little unresponsive. My iPhone 4S and now the S3 show little to no real grease.