UPDATE: since the new subscription model started November 2015, you can also run multiple personal licensed copies at the same time (like on laptop and desktop for remote debugging client/server apps).
You are able to use your license on any number of computers (and under different operating systems).
However, IDE checks for the number of running copies on the local network when starting. In case it finds any copies started with the same license, they are all shut down except the last one.
Here is the relevant quote from the licensing agreement:
(a) Licensee may:
(i) install and use the version of the Software that has been specified in License Certificate on multiple Clients and operating systems, provided that a number of concurrent users never exceeds the number of Authorized Users specified in License Certificate and that the same License Key is not used concurrently by different Authorized Users, on different Clients or operating systems;