You can get both User CALs that cover a specific user on any computer that they may use (think execs with a Desktop, Laptop, and WinCE device) or Device CALs that cover any number of users accessing the system from that one device (think common-area computer, shared workstation for multi-shift information workers)
We do a mix of Device and User CALs. We have a few workstations that support 3-5 graphic designers and machine operators with different schedules throughout the week and over 3 shifts a day, these workstations are perfect for Device CALs.
We also have some shared use computers for production floor employees (who also don't have dedicated desktops) to log their time and lookup production information shared by 5-10 different users, we use Device CALs for these as well.
For pretty much everyone else in the company that has a dedicated desktop and/or laptop we use User CALs.
For 30 users this distinction may not be worth the trouble but it saved us a considerable amount of money since over half of our workforce are manufacturing production employees without dedicated workstations.