As discussed many times in WPW, this is actually a falicy for many reasons.

1> With all other things being equal (links/content), validated Xhtml and CSS designed websites have equal chances on being top ranked as it's counterpart (within reason of course).

2> Although, design as in colors and image placement in itself, may not affect the rankings, the design can have a negative effect. In the past, I have been given full site photo shop files, which despite my objections were to be sliced and created into websites. Sure, you can work and get the valid xhtml, but if the content is all contained within the images, then there will be problems. So yes, in some cases the design does effect the SEO.

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But back to the original post.

When working with designers or anyone questions something, I simply tell them "function then form".

I tell them that print [graphic] design is different from web [graphic] design. When working in the web world, there are more things to take into consideration, compared to print. A lot of times, I get good designs, but the functionality displayed in the design isn't consistent, it's difficult to understand or difficult to even follow.

Overall, I think the problem that I have had the most is the fact that most of the designers that I work with are from marketing firms who are strictly offline marketers (as in print, tv etc...). They don't understand usability and load times.