Having had the HTC Sensation in-hand for about a week, our unit has developed some troubling issues with its touchscreen. Namely, the panel often misses first presses, and also struggles with fast brushing movements.
The first issue results in great frustration when typing, as auto-correction of words does not work without the first letter. It also means you often have to tap several times on icons on the homescreen to launch an application.
With the second problem, the malfunctioning results in very choppy scrolling, in the app drawer or in Twitter applications such as TweetDeck. Frequently the touchscreen will register a brushing touch as a press, and will select whatever your finger happened to be passing over at the time.