An acid test is something that proves whether something is good, effective, etc, or not. The Acid2 test is a test page written by the WaSP (The Web Standards Project), a "grassroots coalition fighting for standards that ensure simple, affordable access to web technologies for all." The test is made to help browser vendors ensure proper support for web standards in their products, and it even contains errors deliberately to ensure browsers handle those properly.
We are entering a new era for the web. With stronger focus on dynamic content on the client side carried out transparently providing extensible interfaces for end users (AJAX), a strong emphasis on the use of open standards and generally putting the burden on browser implementators rather than on black magic done by web developers, the web is moving forwards. The time were you needed to tailor content for browsers, their specific behaviour and bugs, and other quirks is almost gone.
As more browsers are pouring in with support for the Acid2 test and in general embracing open standards pushed by the W3C, developers can concentrate on making good content using well-defined standards. Gone is the duopoly of the 90's where you had to choose between bad or worse. Users can choose between various browsers that support open modern standards, on different hardware and different operating systems. Browser vendors can compete on user interface and good implementations rather than to rely on users in bliss accepting 10 year old technology as being the web.
So, wether your browser of choice supports Acid2 or not, at least make sure it embraces open standards and allows you to take advantage of what the web has to offer today and in the future. Don't miss out and ditch your stone age browser in favour of the new shiny ones that are developed by people that care about the web experience. Don't accept that your favourite web site is behind with features because its developers thinks writing specifically for ancient clients is good. Help the web evolve and vote with your buck, or at least with your bandwidth.
For a stable and rich web experience download Opera 8.53
Curious about the future? Check out Opera 9 TP2 or one of the weekly builds with leading edge technology incorporated.