[saurik]

People generally don't read HTML... machines do; the further levels of validation you can obtain (and certainly to the extent to which the code is somewhat valid at all, such as making certain to have tags that aren't misusing quotation marks or brackets or entities), the more likely your code is to be understood in the same way by random implementations of HTML parsing that may be used in the field.

[zalew]

yeah, I remember injecting flash objects with javascript wrapped in cdata, so the w3c validator confirms my awesome coding skills in green, good times. now I treat validators as useful tools for double-checking syntax, and nothing else. it validates more often than not anyway, but it's not that I care.

invalid code doesn't mean shitty code, and the other way around - being valid doesn't say anything about the practical quality of code. know your craft = know the rules + know when you can break them.