While Acid2, released three years ago, focused on CSS, according to WaSP's press release:
Results posted around the web show pretty bad results for the current set of browsers, with Firefox 2 posting in the low 50s, IE7 posting in the low teens, and Opera posting mid-40s. On the other hand, nightly builds of the upcoming Safari and Firefox browsers are posting in the 80 - 90 range. However IE8 is only, according to reports, scoring in the high teens.
The Acid3 Test is designed to test specifications for Web 2.0, and exposes potential flaws in implementations of the public ECMAScript 262 and W3C Document Object Model 2 standards. Collectively known as DOM Scripting, it is these technologies that enable advanced page interactivity and power many advanced web applications such as web-based email and online office applications.
As a series of 100 mini-tests, Acid3 has already been found to expose flaws in all tested browsers, including Internet Explorer, Firefox, Opera, and Safari. WaSP hopes that Acid3 will prove useful to browser makers during the development of future versions of their products.
It should be noted that this test is a standards test, and it's what browsers should aspire to, but we all know they're likely to fall short - though low teens (IE7) is a little much.