Conditional comments or IE specific hacks

So in my interweb travels of evaluating other programmer's CSS I've noticed a bunch of people using the underscore or asterisk hack that is vendor specific to IE browsers for debugging purposes though W3C does not parse this as valid CSS.

I personally prefer comment conditionals where you can at least defer to IE specific CSS that is valid but I guess the only issue with that would be addition of extra CSS.

So I'm curious about a consensus of what you prefer and the positive or negative implications of each method.

Comment conditonals or IE vendor specific hacks?

PS - Honestly this should be titled do you support IE layout or not :-)

Solution

Conditional style sheets are the way to go. The word hack itself implies that you're doing something that you shouldn't. But a few short words on both:

Conditional style sheets

(+) Cleaner CSS code
(+) Easier to manage
(+)Easiey to understand for other developers
(+) CSS validates
(-)More CSS files (thus more server load)

Hacks

(+) Faster (possibly)
(-) Messes up your CSS
(-) CSS doesn't validate
(-) Very unclear for other developers (especially non-experienced one's)
(-) Could cause problems with newer versions of IE