I have been using Joomla for quite sometime now and I just love the flexibility of this content management software. But I notice that I get a huge load of W3C XHTML Errors when I validate my page. On the other hand, when I use the latest Firefox, IE6&7, Opera, I still view it as normal. I get response from some people saying that they couldn't view the page properly.. I don't get it.. are they using the older version of browser or what? The people who couldn't view is a very minor group.. very small group... So what's the importance of this W3C compliance thingy? My sites are MichaelWoo.net and DotMySpot.com Need feedback! Thanks!
None what so ever - it is best practice not required practice. Your code would need to be truly terrible for it to impact SEO or other non-user aspects and on the other hand perfectly valid code can display incorrectly in different browsers (esp those designed for disabled people) because of the different ways that different browsers interprit the same code. It is good to be compliant from a "feel good factor" and it does encourage good behaviour but isnt work beating yourself up over unless you are a web designer who's selling point is compliance.
Joomla can be fully compliant to standards - it's all down to how you code your templates. For an example check my site (sig below) which is a standards compliant Joomla build (apart from a single CSS declaration to do with Apple iPhone/iPod performance - so it isn't recognised by the CSS validator yet). I regard validation as pretty important. Not only does it mean search engines have an easy time spidering your site, it also shows your a committed and efficient coder .