I've never lost or damaged a cell phone yet so skipping the insurance was a no-brainer. A week after owning it, the Droid popped out of my swivel holster as I was exiting my truck. It fell on it's face on an asphalt parking lot. Lots of scratches and the edge of the glass is chipped in three places. One of those chips has now developed into a crack.
I feel like the Droid is bigger, heavier than any other phone I've had, it's more likely to fall at some point. Due to it's mass when it does fall it's going to take a harder hit.
I called in and added insurance to my account. I know for sure I'm going to need to use it soon, as more cracks develop. Once the phone is a year old and the retail cost for a replacement has come down, or Droid v2 is out, I'll drop the insurance or upgrade to a new model.
I think it's wise to carry the insurance for the first 6 months or so, until you're used to the heft of this phone, had some experience with dropping it, and are truly comfortable in thinking that you could never damage it. You can cancel the insurance anytime you like.