Share your experience!
I noted that the response of the screen is a bit odd. For example, when I'm typing fast, the screen won't respond to my press on space bar and thus making my msg strange. After some search, I notice that a few reviews have mentioned the same problem. So it seems that it's not just that my device is defective, but in fact an universal problem? Anyone is facing the same problem with me?
Please see below review for a more accurate description of the problem:
http://m.androidcentral.com/sony-xperia-x-performance-review
Honestly I really love that phone. The camera is so fast, the fingerprint lock works so well, the screen is so great under the sun... But if I have problem using whatsapp, then I really have no choice but to sell it and get another brand's... 
Hi scalkie, I don't know how to describe it. It's like, when I'm typing "I don't know", it wouldnt record the "space" and the "o" such that the text becomes Idn'tknw"... I need to deliberately press hard on "space" and "o" to make it appear. I also notice that when I select words near the edge of the screen, it wouldn't respond even I've pressed 3 / 4 times, I need to press long to make it typed out...
I have owned two Sonys (M5 and X), and both of them have the same problem with typing.
I am assuming that sometimes it is actually too accurate, especially when your thumbs are too close to the screen, it will detect your other fingers as a swipe motion.
Try disabling the Gesture input. Try lifting up your fingers higher after you press a key.
Sigh... After using 1 month, I still couldn't get used to this non-responsive screen... I can't tell how much I'm regretting now... I'm pretty sure that I won't buy any Sony phone again.