Opera 10.5 and newer has a built-in plugin blocking feature, similar to FlashBlock, that you can enable at opera:config #Enable On Demand Plugin and #Enable On Demand Plugin Placeholder. That will show a placeholder that you can click on, instead of just running the Flash/Java script embedded in the page. That will avoid intrusive flash adds and make loading pages faster, and it will also increase your privacy, as I’ll describe.
Most browsers are uniquely identifiable because of the their combination of brower version, plugins installed, fonts installed, computer screen details and a few others. http://panopticlick.eff.org/, a website set up by the Electronic Frontier Foundation, shows how identifiable your browser is. As it appears until now, the feature that is most useful for uniquely identifying a browser are the installed fonts. Opera was the only browser that did not send the font data that uniquely identifies my brower, because of not running any Java/Flash without me requesting it*. I had however a unique combination of plugins installed (one of them is extremely rare on Linux, I may be the only one that has it installed and also tested of Panopticlick).
I must thank EFF for running these campains in the benefit of the Internet users, this is a particularly informative. Please test and spread the word. Given that the receptivity of browser makers increased lately because of increased competition, this EFF campain** will likely have effects in a not too far future.
This also shows that Opera puts its users’s interests before the interests of Intenet companies. Obviously, websites are not happy when their most effective adds are blocked, but there’s only so much some people can accept.
*Probably a console oriented browser, like Links, would reveal a lot less information.
**They actually call it a research project, but I believe it will have some important effects.