The w3c is a consortium for an open and standards complaint web. This is important as it lets every browser render sites properly. Following these standards mean a more reliable and stable web, less downtime and bugs, and lets people who cannot or will not use a newer browser. For example screen readers work best on a site that follows the w3c while it will not work as well or not even at all if it doesn't.
Using browser specific CSS is also bad. This means certain browsers will not work and you have to spend more time to fix the issues that arise from it. You also double the work since you must have workarounds for browsers that do not support the browser specific CSS. You also increase the chances of bugs and performance issues with various browsers, not to mention you break compatibility with older browsers and screen readers.
Now that being said you may be wondering why I'm mentioning this. Maybe you're not and that is fine too. The reason why I'm mentioning this is that I'm sick of websites not working when they should if they actually validated their websites and use browser independent CSS as they should be. Browser specific CSS and broken websites are killing the web. They're slow, full of bugs, and only work on a handful of browsers.
I mean seriously! How can a website with multiple developers cannot code a site properly(Looking at you deviant art web developers) and there is me, someone who sucks at HTML, CSS, AJAX, and all that make a site that will not only pass validation, but work on 99% of devices from the Amiga all the way to a ZX Spectrum and everything in between.
Seriously though. The homepage for Deviantart has 404 errors and 7 warnings, and this doesn't include the browser specific CSS errors. Here is the link if you want to see for yourself. Now my site which isn't as complex as this passes. Here is my site, passing the validation. Also for those of you who think it isn't fair, the w3c's own site which is complex also passes.
Until the issues are fixed I am looking for a new place to have my art. I will still use dA since I have no choice, but I will not be on much.