I would have suggested using Regseeker to search your registry using the term "Opera" and try to manually clean out all references, but I just took a look at my Zsoft Uninstaller installation log, and noticed that Opera installed a load of registry strings. Many are in areas of HKLM that have no reference to Opera and would be very hard to find. That's why I find to hard to believe that Revo can actually find all these registry strings that appear to be otherwise unrelated.
Dennis said he had this problem with Opera even after reinstalling Windows. Those registry entires would have been wiped than.
As for Revo it doesn't find anywhere near the info that Zsoft records during an install. I have checked this on several programs that I have uninstalled with Revo. I check what Revo finds against what Zsoft recorded and there is a big difference. Even when I set Revo to the most aggressive settings it doesn't find nearly all the entries that Zsoft records.
When you uninstalled Opera, before reinstalling did you make sure all references to it were deleted in your Documents and Settings folder?
Maybe try installing for a single user that way no folders/files are installed in that folder. You are given that option during install if you use the "Classic Installer". I don't know if that option is available with the Windows Installer version which I have never used.
Dennis which installer did you use? Try the other maybe it will make a difference.