I've been going back and forth with Microsoft on an issue that has been bugging me for a while. Whenever I try to use the Export-Mailbox command on my Vista workstation, PowerShell crashes. This is with a relatively new (less than one month old) Vista install and having re-installing PowerShell and the Exchange management tools. Yet, when I try it on a co-worker's workstation, it works fine.
Finally, Microsoft PSS hit on something that allowed me to find a workaround. After turning off UAC, I could run Export-Mailbox without it crashing PowerShell. Oddly enough, UAC is still active on my co-workers' workstations where I was able to successfully use the command, so the problem is clearly more complex.
Another clue from Microsoft: check the permissions on the registry key "HKLM\Software\Microsoft\Exchange\Exchange Migration". Based upon running TTTrace, I was getting an Access Denied error while trying to hit that key, resulting in the freeing of an internal structure needed to write data to the Application Event Log. The account I was using was a member of a group that was in the local Administrators group, which in turn had Full Control on that key. Perhaps that wasn't sufficient. I gave my account explicit Full Control on the key, turned UAC back on and rebooted. Export-Mailbox worked with UAC on.
Update A further clue: My co-workers were able to run in the command with UAC active and without explicitly giving themselves permissions on the registry key because they were running with elevated permissions, thus sidestepping UAC, whereas I was simply logging in directly to the workstation as the privileged user.