[anthonyb]

If a site doesn't validate, it might not appear properly in some browsers, reducing your customers' experience of your site. In extreme cases, it might also mean that they can't (eg.) see your buy button, killing your sales.

[timdev2]

Validity is completely orthogonal to utility. It's trivial to craft a broken page with an invisible buy button that validates. I don't know of any major ecommerce site that validates.

[anthonyb]

No, it's not. You might as well say that it doesn't matter if your programmer doesn't use version control, or your surgeon doesn't clean under his nails.

Major e-commerce sites will have tested under every major browser anyway, so invalid HTML won't matter so much to them. Smaller shops don't tend to do as much testing, so it's more important that HTML validates.

[hammock]

So what you're saying is it doesn't matter if the HTML validates as long as you test well.

[anthonyb]

How many one man dev shops (which is what we're talking about here) test well, or even in in multiple browsers? So yes, if you get a web site from a one man web design shop, then you should make sure it validates.

If it doesn't, it's probably rendering in quirks mode, and you'll have all sorts of problems with the layout if you need to change it.