I have found what is probably a bug in Vista and/or Windows 7: when
copying EFS-encrypted files to a different computer without EFS
performance is severely degraded. This is caused by 30 second timeouts
during which the copy target looks for non-existent domain
controllers.

I have described the issue and a workaround in detail here:

http://blogs.sepago.de/helge/2009/12/16/the-30-second-file-copy-bug-or-efs-bad-performance/

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Please visit my blog at http://blogs.sepago.de/helge