As stated in the Creative Suite CS5.5 EULA you are permitted to install ONE copy of Creative Suite on your primary computer, and one additional copy on "a portable computer or a computer located at your home", provided this copy is not used at the same time as the primary installation. This is different from the idea that you can install it "on two computers" - you have to think of it as one copy being used in either of two locations, but never both. Installing two copies on desktop machines is not permitted unless one or both of them is in your own home.
Creative Suite is sold and licensed as a single product (it has a unified serial number and the member applications cannot be transferred out of the Suite) so the rule on simultaneous use applies to any combination of the member applications. If your primary computer is running Photoshop, your home computer or laptop cannot run anything. This applies whether or not you're sitting at either machine (so leaving an office computer rendering out a video sequence overnight counts as 'in use').
