Tim Bray speaks on the benefit of dropping support for version 4.0 browsers and below.
- You can cram a lot of the styling information into CSS, which gives you better, more professional-looking pages, and makes them smaller and faster.
- You can cut out a lot of design compromises that are probably lurking in your HTML-generation code.
- You can ship valid, well-formed XHTML, which may surprise you by coming out usable on a variety of non-PC wireless devices right now today.[ongoing]
Personally, if you’re still using a version 4 browser, you’ve got issues and you need to upgrade. I will not, and do not, build just to support your backwards compatible ass.