As long as the other user is under your account, you'll be able to view the user activity information in a few areas. Also, once you add a user you can determine if they are an Admin or a User, with a User having reduced privileges under your Admin Settings.
Furthermore, you can also edit the user and limit them to only be able to view records that their user is the contact owner of. This can be done under Profile > Settings > Users, you can edit the user 'Record Access' by clicking on the 'Edit' option under the 'Action' column.
On the sequence page, you will be able to see and filter for the 'Creator' of sequences. On the Sequence list page, high-level statistics will be displayed, and you can click into each sequence for more detailed statistics respective to that sequence.
Under the Reporting Module, you can set up different reports, etc by an individual with emails sent, replies, calls, tasks, etc.
Also, we are working on a dashboard enhancement that will allow you to easily filter through different data points by timeframe, as well as by user. Stay Tuned!