Be aware that Youtube is not using only flash player to render videos. Its using also one different codec. so when we are talking about Hw acc enabled and HW acc disabled we MAY or MAY NOT be talking about two completely different codecs... if you want to render anything on idle vram clocks, you need a lot of time. usually idle clock is not enough to perform all tasks so its better to clock them up.... In the past changing of clock on CPU using multiplier, and decreasing CPU voltage resulted in very interesting behaviour called VDROOP. In this situation, if CPU finished task, it clocked down. First voltage went UP and in few miliseconds went down to IDLE. This required change in Intels VRM, but still - you can write some bastard code which require cpu to clock up and down. With a bit of luck you can cause system to crash. I decided to prevent this problem. My CPU is clocked to fixed frequency and set to fixed voltage. However I have not such control over GPU. Good code clock GPU to 501Mhz, and memory to 1375Mhz (in case of my Hd7970), and keep GPU clocked like this for few second AFTER the task is finished. This cost bit more energy, but its safe. If I want to spare as much electric energy as possible and i am stupid enough i will write code which sets GPU back to idle immediately when the task finishes. However... GPU can be multitasked. So if Task 1 sends a request to clock down, while Task 2 is still executing we got a problem. This can be a problem even in situation when Task 2 tries to start too early after Task1 was finished, because switching from from 501Mhz to idle and then back takes some time, changing voltage took even much moretime (few miliseconds). This perfectly fits to situation where my Opera is working well, and other browsers are screwed. However I dont have direct access to code they are using, so its only rought description of the situation I have seen.