I watched the Brent Ozar, PLF Scary SQL Surprises webcast and was surprised by him mentioning this bug: http://blogs.msdn.com/b/ntdebugging/archive/2009/02/06/microsoft-windows-dynamic-cache-service.aspx
The blog references another blog and talks about the problems with x64 systems and the file caches. Too much file copy activity on your x64 server can severely crunch your memory, including your SQL Server memory.
There’s an unsupported utility available from MS in the blog you can get, but I like Brent’s advice better.
Don’t copy files on your production SQL Server.
Use another machine to do the copy work for you, even if it’s slightly slower. That includes watching out for ETL work and any jobs on your system that might do the copies for you.