You can effectively manage the multiple sites in your account by using the 'Grouping' feature to club each of your client's sites into separate groups. For example if you have 50 sites in your account belonging to 3 different clients, you could create 3 separate groups, naming them 'Client 1', 'Client 2' and 'Client 3' under which to club their respective sites.

To create groups for the existing sites in your account, you could go to the 'Edit a Site' section and click on the site(s) you wish to group. Under 'Site Group', choose 'Create New Group' from the drop down box, enter your group name and click on 'Save Group'.

When you add a new site to your account, you will need to click on the 'Grouping Options' link, found on the right side of the 'Enter Website Details' tab. From the drop down box next to the 'Select Group' option, select 'Create New Group', enter a group name and click on 'Save Group'.