If you install YourSites directly on the client sites (as opposed to doing this in batch from an existing online service) setting up the secure connection between the 2 sites allows you to login to the backend of your client site simply by clicking the link in the list of sites in YourSites.
Note that you will be logged in as the user who installed the plugin - this can be changed by editing the site entry in YourSites and changing the 'Remote user id' field
Note that this direct login can handle backend access controls using htaccess username/passwords and should work with plugins that set and access key for backend access to your site (though we have only tested a couple of these plugins).
We love every single one of our users, without you YourSites simply couldn't happen! So we would love a review at the Joomla! JED so we can let others know about us too, please take a minute to write a review:
If you feel you have something negative to say, we would implore you to speak to us first, as we really really don't want anyone to be unhappy!