You cannot get clicks on Tablets to make the onClick callback when clicking across different buttons at a reasonable speed - major problem.
Using Generic Forward Composer and standard callbacks of onClick$_buttonName(Event event) it is very easy to get a visual click response on the button (it flashes color) but no callback. As part of researching this problem I did find a site which states that there is a 300ms delay in onClick's on Tablet Devices. This would explain the problem. To get around this issue I am now using onMouseDown and a zAu.send to handle my callbacks so they happen immediately. The onClick delay issue is really a major problem in our application and is easily reproduced. This is not a ZK issue in that straight HTML components experience the same delay - not just ZK. I wrote a plain HTML page that has a row of 10 buttons. When they are clicked change the color of the button to red, if you click fast you will only get 6 or 7 out of 10 every time.
Here is a link to a site that discusses this issue and has a JS lib to solve it - I have not tested this JS Library to see if it works.
Attached is the simple html button test file which demonstrates the slow onClick behaviour.