The Adobe Creative Suite EULA (End User License Agreement) permits two installations and activations per copy of the retail product (whether purchased in a retail box or by download), but those two installations are for the purpose of a single user having access to the software on an office computer and a home computer or mobile computer. It is still a single license for one user.
Thus, if you have two separate users, they require two copies of the Adobe Creative Suite. For a third user, you need a third copy/license. For larger organizations or multiple licenses, Adobe does have volume licensing plans (see http://www.adobe.com/go/gffooter_licensingprograms).
Hope this helps!