I simply created a new project folder and connected it to Unity Asset Server to bring in a Unity iPhone 1.6 project.
After successful import of the project, I created the folder iPhoneStreamingAssets which contains all of my .m4v videos in the same directory as my Assets folder (the correct setup and the exact same as my iPhone 1.6 version of the project)
From there I simply just built to device. The game itself plays fine, but my videos do not play anymore. I played through the Editor using the remote and my console prints the call to the iPhoneUtils.PlayMovie method was made.
You no longer use iPhone Streaming Assets...
Here's a paste from the Unity 3 beta changelogs (you guys should be keeping upto date with this) :)
iPhone: iPhoneStreamingAssets is renamed to StreamingAssets and is now located under the Assets folder (visible from within the Editor).
I did some digging between the builds from 1.6 and 3.0, I noticed that the 3.0 version of the build did not contain the m4v files at all, where in 1.6 they were included in Data>Raw.
What I ended up doing was just copying that Raw folder to the Data folder of the Unity 3 version and then built to device. The videos played as expected.
I'm chalking this up to "Hey, it's a beta." and submitting a bug report.