Users complain that system runs slow when mysqldump is in progress
There is a known issue in Windows, that when you push a large file to another server all the memory ends up getting allocated to the System cache instead of the user processes.  You can look  in the Physical Memory (MB) section of task manager to see how much memory is allocated to the system cache.

This can be solved by backing up to a local disk, then having the remote machine pull that file.