Walking out of a theater last night, I struggled to convey to my wife why I didn't like the movie. "I can't tell you exactly what they could've done better," I said, "I just know they did it wrong." Odds are, 99% of the internet population is clueless about good web design, just as I'm ignorant about creating a good movie. In other words, if you asked them which elements are most important in creating a professional website, they couldn't tell you.
What they could identify, although subconsciously, is bad web design. If a customer perceives that little thought and effort was put into designing your site, they may draw a similar conclusion about your products or services.

While many factors contribute to site abandonment, some research suggests bad site design sits at the top of the list.

What makes a professional, usable website?

* Consistency: There's nothing worse than having to re-learn the site structure on each page. Navigation, headers, and footers should remain consistent throughout the site.
* Logical Layout: Are the most important page elements above the fold? Is site navigation where it's supposed to be, on the left or top of the site? It just doesn't pay to get too creative with your site's layout. Checkout the artistic, yet highly confusing layout of Crumpler Bags. After you sit through the unwelcoming splash intro, you must mouse over the navigation links on the bottom left of the site in order to decipher their meaning.
* Good Colors: Colors can make a huge impact on the perception of your brand. Ensuring that your color scheme is inline with your demographic is an invaluable.
* Easy Reading: Stylistic fonts are fine for logos and branding, but simple san-serif fonts are a must for content.
* Speed: A usable site that doesn't serve up content fast is pointless.

Websites are tools first, artwork second

I've dealt with many talented graphic artists who mistakenly design a website the same way they'd design print media. It's incredibly important to remember websites are tools first, artwork second. It's very possible for the design of a website to be too good. In other words, the artwork or animations can take away from the core purpose of the site.

How to Know if your Design Sucks

Since we tend to operate in the box, we may neglect to notice fatal design flaws with our own sites. Here's 3 ways to gauge the success of your current design.

1. Ask your customers: The customer knows best. Survey your customers to see what they think of your site design. How do they feel about the colors and layout? What about the pictures and graphics? Ask both open ended and multiple choice questions.
2. Ask your peers: Submitting your site for review in webmaster forums is a great way to get the feedback of other experienced web designers.
3. A/b test different designs: The only sure-fire way to determine which design is optimal is through a/b testing. Tools like Google's Website optimizer make this a cinch.