With the increasing trend of using touch screens instead of real buttons the lack of tactile feedback has become an increasing issue. The response, in some handsets, has been to use strategic vibrations to simulate this, a form of haptic feedback to the user to reassure them that their touch has been registered.
The Samsung Omnia already does this to quite an extent, making the device feel quite alive, but of you want to add it to your other Windows Mobile smartphones, Touch Response, developed on XDA-Developers may just be the answer. The software installs itself rather deeply as a new Touch Screen driver and intercepts Touch inputs, making it potentially quite powerful, for example allowing vibration feedback only when using the soft keyboard but not for anything else. It is however only in version 0.02.1, so use at your own risk
Download Touch Response from this XDA-Developer thread here.