Just a few minutes ago it was announced that Opera will move from their traditional Presto engine to the more modern v8 javascript engine and Webkit html layout engine that's present in both Google Chrome and Chromium... For web developers this announcement cannot come a moment too soon, with the release of HTML5, Opera has been lacking in features that major browsers have and have been a burden for developer's to support for a long time - making the move to the Webkit engine and v8 engine has been a long time coming, with Opera (along with their proprietary Presto engine) seen as "lagging" behind in terms of web interoperability and support.
v8 is currently the fastest JavaScript engine and was developed specifically for the Google-developed browsers, however mainstream usage has extended to other projects such as node.js, a fully functional web server that can be written in javascript, as the v8 engine is open source, more and more projects are expected to use the engine - including Opera.. While Presto, Opera's current and will-be-depreciated engine has performed well in terms of CSS speed and memory management, has notoriously lagged behind in it's JavaScript speed and has not reached popularity outside of Opera because of it's status as a proprietary engine.