A few months ago, a root-only app called Streak Vibrations was the only way to disable the vibration of the capacitive touch buttons on the Dell Streak. Without it, your thumb was at the constant mercy of the buzzer when all it wanted to do was tap the Home, Menu, or Back buttons.
Now that Dell has released the official Android 2.2 (Froyo) update for select Streaks, however, your thumb can regain some control and decide whether or not it wants to be buzzed without the help of root access or a third-party app. To disable the touch buttons' haptic feedback on your Froyo-ized Streak, simply tap the Menu button for one last buzz then press Settings -> Sound. Scroll to the bottom of the list and tap the box to uncheck it.
If your thumb discovers that it feels lost without the reassuring vibration, then just tap the box again to re-enable the feature.