Hi,
Currently what we are seeing when impersonating a customer or the customer is logged in and you goto some tabs or try to edit something that it hangs and then you maybe get an error or missing data on a page.
It really needs maybe a message to say something along the lines of "Site currently being backed up some features may not work while this is in progress" or whatever and lock what will not work/show correctly etc.
Something along those lines anyway just so clients are aware of what is happening.
Thanks
Paul