The YUI article on
graded browser support is a nice overview of the nuts and bolts of browser support in a world where different browsers provide different levels of support for web content. It links to a
chart that shows how different browsers are currently supported.
Browser support is a nice example of a class of strategic issues that are surprisingly prevalent on web projects. This is small 's' strategy: web developers don't need to understand your business model or care about financial engineering, we just need to know which users we _must_ support, a business/technical question that will determine which browsers we need to support well, which browsers we should support on at least a rudimentary level, and which browsers we shouldn't worry about.
The standard scenario is the business owner (aka stakeholder) of a project asks for tricky functionality (and this could be something as simple as fly-down menus or precise layout of text and images on a page) and, when asked about browser support, asserts that 'all browsers' or 'all major browsers' should be supported. This is usually about ten minutes before the business owner expects to head out of the office on vacation for two weeks, and before she goes she wants a firm commitment that the project will be completed or at least well underway when she gets back.
My job is often to try to figure out how to share the unwelcome news that there are some basic business questions that need to be thought about fairly carefully in order to make sure expectations are met when the site is completed. They involve thinking about people who turn of javascript (no fly-downs), accessibility (how should keyboard navigation work? Where do we need alternate content), maybe even localization (You can bet that somewhere on the carefully laid out page, localized text just won't fit without blowing something out or wrapping in a surprising way).
And of course there's the unwelcome news that we don't plan to test on IE 5 and a number of other browsers, and that people using these are likely to have difficulty with the page in proportion to the complexity of the page.
This problem is about to get worse, not better: with IE 7, Firefox 2, Ajax, and Web 2.0 we've got a new generation of browsers, some wonderfully tricky client-side technology, and rising expectations from stakeholders as to the kind of experience we can deliver.
This means a lot more conversations ahead about which browsers we need to support and which browsers we will disregard to some extent.