I've managed to get the CPU usage back to a reasonable level, so I apologise for wasting time on this without properly testing.

I re-installed flash and restarted the computer - it's gone back to 14-30%, spiking up to 40%, on media content and video playback. Strange, since I did re-install flash before I posted this thread (but didn't feel the need to restart the computer, only the browser).

Some update must have caused the issue.

I agree with you Harrision about flash's cross platform nature and lack of dedicated and optimized hardware acceleration, I did mention it a few times above.

I still find it strange however how it uses the same CPU power to play a compressed flv file as it does to move around and scale a few images (about 3000MIPS!!! on peak average). It could really do with being optimized better since it's now a standard internet format.

Many emulators take less resources than flash!