The most straightforward method currently is to use SQL Server Management Studio and simply "Select Top 1000 Rows" of the "users" table in "BackupServer" database.
The more advanced, filtered query used above is:
,[UsedDiskBytes]/1024/1024/1024 as TotalStorageInGB
WHERE Enabled = 'YES'
After the results are shown, right-click in the bottom pane and choose "Save Results As..." to save as a .CSV file.
In the future:
There is already a feature in development for adding the ability to synchronize the xSP user list with a CMon instance, which would allow an export to be done through that interface.