1 Bug in 3

1- Safari 3 does not render relatively positioned elements with negative percentage: First demo (semi-reduced testcase), complete CSS columnar layout (Liquid Scroller)

Specific WebKit and Safari 3 bug collection sites

WebKit's Bugzilla bug reports: this is the publicly accessible bug reports on all WebKit products. Thousands of bug reports are available via Bugzilla and accessible to the public.

HTML 4.01 conformance tests by Robin Lionheart. MSIE 7, Firefox 2, Opera 9, Safari 2 and Icab 3 are tested, measured and their results can be compared.
Several hundreds of CSS testcases by Ian "Hixie" Hickson. This has to be the most complete, thorough testsuite for modern browsers.
CSS 2.x testsuite (DRAFT) by Eric Meyer. The results of CSS 2.x testsuite page needs updating for new versions of browsers.
Current CSS 2.1 Test suite at W3C (last updated on August 4th 2007). Firefox 3.0a9pre rv:1.9a9pre nightly build 2007092502 fails 27 tests out of 500 (5.4% failure); Opera 9.50a3 build 9542 fails 50 tests out of 500 (10.0% failure); Internet Explorer 7 fails 129 tests out of 500 (25.8% failure).
DOM 1 Core tests with JsUnit 2.0Beta TestRunner by W3C. MSIE 7 fails 85 tests out of 224 tests, a 37.9% rate failure which is well over/above the percentage rate of Firefox 2 (6.3% failure rate) and Opera 9 (5.1% failure rate).
CSS 3 Selectors test suite results by Robert Blaut
User Agent Accessibility Guidelines 1.0 Test Suite for HTML 4.01 (draft) by W3C's WAI