Opera 10.51 is running on my work PC under Windows Vista, with 2gb RAM and 2.66ghz Core2Duo. There are about 50 open tabs, and one of them is playing a Youtube video. CPU usage is listed in the Task Manager as around 2-3%, with 300mb of physical RAM used.
The most recent Opera (10.10 I think... actually 10.52 was apparently released today, but 10.10 still reports that there are no new updates) on my 2.33ghz C2D Macbook with 2gb RAM in the same configuration except without any Youtube videos playing, uses 10% CPU according to top, and 20-30% with a video playing. And that's with the Flashblock userjs - before it was much higher. Why? Is it because my PC has a half-decent graphics card and the Macbook doesn't?