If you saw the video, just like I did, it was at best blurry and poorly edited. Condolences aside, there are some significant anomalies and "fishy circumstances" surrounding Nick Berg's murder that cast enough doubt on it for even the least skeptical to take a second look.

Kuro5hin has 50 listed and detailed, including why Nick Berg was wearing an orange jumpsuit similar to those worn by Iraqi detaines in Gitmo and Abu Ghraib, that those weapons brandished by the "insurgents" were actually Israeli made and not AK-47s, the origins of that Monobloc chair, and, if these really were "insurgents" running from the U.S. military living in caves and tunnels, why they all seemed to be a bit overweight.

Of course, there's the strange timing: Nick Berg's captors killed him (at least on video) as a retaliation for the "shameful pictures" of Iraqis being abused at Abu Ghraib. How could this be if, according to the news reports, Nick Berg was killed two weeks BEFORE these pictures were made public?

Worth reading the long entry, including the comments and the links.