I keep my vibration off because I try to keep my battery running as long as possible. Every vibration will ultimately drain the battery and will eventually deplete what resources the battery has to offer.
I recently switched from the iPhone to the Droid Incredible and love it! I hope this post helps the owners of the previous posts, or anyone else looking for a solution.
I found this information on another website - Credit: Motorola Droid: Enable/Disable Vibration When Pressing Keys
1. From the main screen, press Menu
2. Select Settings
3. Select Sound & display
4. Check Haptic feedback
on or off.