If there's an safe and relatively quick way to change your bitcoins into USD or Euros or any other currency, then it would be easy to spend them on Amazon anyway -- as an end-user, you might even semi-automate* the conversion when shopping at such sites.
*Presumably you would want to at least sign off on the current exchange rate first.
Tangential, but a subject of some local interest:
Why Bitcoin will fail by Avery Pennarun. "The sky isn't red." Thesis:
I'm not sure I buy these and am not competent to evaluate his claims on 3., but would like others' critique.
L019: Bitcoin P2P Currency: The Most Dangerous Project We've Ever Seen by Jason Calacanis. A rather more enthusiastic viewpoint of the project:
The actual text contains many more caveats than the eye-catching selection of points above.