Windows 7 - easiest way to tell whether AERO / DWM is enabled?

There is a corresponding service UxSms (Desktop Window Manager Session Manager- Provides Desktop Window Manager startup and maintenance services).

This starts a process dwm.exe. With this started, AERO is enabled (if stopped AERO is disabled). So basically if the process dwm.exe runs, AERO is enabled (read the comments, this means that AERO themes might, but not necessarily have be used. However, without DWM no AERO).

Run SystemPropertiesPerformance.exe, options 4-6 in the long checkbox list of visualfx