Not too long ago I insisted that we support Internet Explorer 5.x. I argued there are still a lot of people using the browser and making our website work for it is not optional. Now, I changed my position.
The only bug I encountered in IE 5.x is the box model problem, wherein it miscalculates the total width of container when padding and/or border are added. Fortunately, there is the Box Model Hack by Tantek Celik, which takes advantage of a CSS parsing bug in IE5. By implementing the Box Model Hack, the browser takes precedence over the standard and that puts your website at a disadvantage.
There is a good article here on the advantages of developing against a standard, among them:
Short-term cost savings
- Less development hours
Long-term cost savings
- Dramatically lower bandwidth costs
- Simplified, fast maintenance
- Any knowledgeable developer can understand and alter the code
- Fast to market
- Rapid, site-wide changes for re-branding efforts
- Tremendous search engine optimization
- Pages load quicker and are more responsive
- Cross-browser and cross-platform compatibility
- Increased accessibility for disabled users
Standards-based approach offers a lot of benefits. On top of that, I agree with the folks at 37Signals that legacy support is not the way to build a forward looking product.
Should you start including "best viewed in IE6, Firefox, Safari" in your webpages? Not necessarily. The most important thing to do is to map out a strategy within your organization on how to adopt web standards. If you need to make a case with your team and upper management, you can start with the benefits I mentioned.