I noticed that in the upgrade to 10.4.11, something broke -- sudently, BOMArchiveHelper would no longer unzip a .zip archive on a mounted SMB share. So I copied the BOMArchiveHelper.app (ion /System/Library/CoreServices/) from a 10.4.10 installation over to the 10.4.11 installation. This fixed the problem.

[robg adds: I can't confirm this issue, so if you can, please comment. I never like recommending replacing system components, but in this case, it seems it may be a necessary evil to resolve what appears to be either a bug or an intentional behavior change. I would strongly recommend keeping a backup copy of the new version, however, just in case unforeseen problems develop. As with any hint such as this, be aware that you're changing system files, and anything bad that happens to your machine is your responsibility.]