The BlackBerry Storm mobile phone is without a doubt the most frustrating touchscreen phone that I've used. Unlike most other phones, the screen itself actually depresses, which means that until the user pushes the screen in, the phone only records basically the equivalent of a hover event. This somewhat simplifies the logic for scrolling (no accidental "taps"), but slows general use--especially in the case of using the on-screen keyboard. Not only does the user need to navigate the keyboard via the touchscreen (generally more prone to errors than a proper physical keyboard), the user needs to push the screen in to record the selection and wait for the screen to return to its normal position before selecting another letter. If the user wants to make multiple selections (such as typing a moderate-length message), this significantly slows the typing rate.
Do you stay awake at night, thinking of the things you should worry about?