I rolled out IE8 to a group of test users in our organisation overnight, and after logging in in the morning, several of the users reported the error
Userinit.exe error and explorer.exe error - iertutil.dll not found
After clicking OK, the PC just hangs with the background visible.
A few people are reporting this error in various forums, but "do a system restore" is not a good solution. We can easily roll back to IE6 by replacing the DLL, or by uninstalling IE8. We just need a flawless rollout!
We're on Windows XP Service Pack 3.
Edit: We deploy via SMS. Initially we had 2 machines with the error, but somebody made a mistake with the test package and it rolled out five nights in a row. By the end of the five nights, 4 more machines had developed the same issue.