The Photoshop individual license allows you to install the program on two computers. However, the programs cannot be used simultaneously. A quick note: the two computers must be running on the same platform. For example, you can install on two Macs, or two Windows machines, but you can't install on one Mac and one Windows machine.
Here's a quote from the from the Photoshop CS6 terms and aggreements:
2.1.3 Portable or Home Computer Use. Subject to the important restrictions set forth in Section 2.1.4 [having to do with volume licensees], the primary user of the Computer on which the Software is installed … may install a second copy of the Software for his or her exclusive use on either a portable Computer or a Computer located at his or her home, provided that the Software on the portable or home Computer is not used at the same time as the Software on the primary Computer.