In your experience, what are the "real world" consequences of using a stylesheet that does not pass the W3C CSS Validator?

Lower search engine ranking?

Difficulty for other devs to interpret?

World hunger?

I am the only person editing my CSS, and I prefer not to separate it into an "ie only" file. I use a lot of the following, which does not validate:

div {
    zoom: 1; /* proprietary ie */
    _color: greenish; /* proprietary ie6 */
    *color: orangish-yellow; /* proprietary ie6 and ie7 */
    -moz-border-radius: 5px; /* proprietary firefox */
}