I have an O2 branded version of the Kaiser. I have installed various of the cabs for HTC software available on this forum - which is excellent, by the way - and was very glad to find an "X" button solution.
Unfortunately, the device then started to crash whenever I closed a program for the first time and had to soft reset. I got a message saying that there was a problem with the shell.
As it stopped when I uninstalled HTC X Button, I am 99% certain that it was source of my problem. O2 stick a program manager in the system bar. It does not add X button functionality, but it does allow manual closure of a program. It does not appear ion any program list, and cannot be removed or closed itself, so I assume that it is part of the rom (not that I am an expert!)
Can anyone confirm this problem, and/or suggest a (preferably freely available) X button program that does not cause any issues? Alternatively, can the (fairly useless) O2 program be removed or closed without replacing the rom?