An article located at http://etech.eweek.com/content/web_technology/top_web_developer_mistakes.html makes really good reading. It's a slide show, but below is a condensed list of what the article says!
My additional comments are in dark blue, you got any?
1) Click, Click, Click - This is great, someone is at your site and they're ready to make a purchase. Here they go; one click, two clicks, three clicks, just one more! And.... they're gone. Maybe if they could get to where they wanted to go right away you would have made a sale. (I disagree slightly in that as long as the navigation is logical and correct then it should not matter to the user how many clicks...)
2) Just Click on the Magic Compass - It's great that new web technologies make it possible to add lots of cool new navigation and interaction techniques. But don't put access to important features and content behind a strange graphic or icon. People know how links work on web pages. Some icons might as well be in elvish.
3) Don't be too Graphic - The Following Web Content Contains Massive Image Files and Graphics That May not Be Suitable For Visitors With Anything But the Fastest Possible Internet Connections. Toning Down the Giant Graphics Files Is Advised For Site Developers. (This is becoming an increasing problem given that mobile internet is really taking off!)
4) Registry of Lost Web Sites - The legend of the Invisible Web Site. Unseen by search engines, web users or anyone who might actually use the services of the website. It uses the magic of enforced site registration to keep its valuable content hidden from all who might want to use it, especially those who want to give the owners of the site some business.
5) Sticking to the Script - Scripting languages are so useful. They make it possible to do lots of cool things in web design. Click this link for an example. Mmm, getting a script error. If only there was some other way to link to content, you know like an HTML link. Don't use scripting where HTML will work just fine.
6) Too Rich - Animation is great, when it comes to Saturday morning cartoons. On the web too many animations, Flashy graphics, spinning graphs and windows popping in your face is sort of like a sign saying, "Stay away". (100% agree)
7) Welcome To Our Site "image placeholder" - Here's a great idea for the budding web site and application developer. There's this technology that makes it possible to display information to visitors and users. It's called Text! And unlike images and animations used where text would work just as well, text will always show up.
8) What's Your Color Scheme? - Whoa, trippy man. I love the way the orange text looks on that purple background. Dude, that financial firm is just going to love this site design. Or probably not. Unless you're designing for a jam band or some other client that likes wild colors, stick to color matchings that are pleasing to everyone. (Obviously they didn't see the custom colours that I used on the TtG Brokers site 
)
9) Directionless Navigation - Wow, this site looks like it has lots of great content and products. But where is everything? Can't find related content? Where's that thing I saw the other day? I'm lost! Users of your web site shouldn't need a trail guide. Make navigation clean, simple and easy to find. (All computer users are very aware of hierarchical navigation [Windows Explorer] and also an address bar 'bread crumb', so play to their strengths!)
10) Can We Table This For Now? - Aren't tables great! They provide so much flexibility when laying out web content. And it looks so nice, at one specific resolution on one specific browser. At other resolutions, yuck! When using tables make good use of percentages and make sure the design looks good on all users screens.
11) Sloppy with Text - Wilcom too my grate neww web apliccatiun. Im a perfessinal web dervelper! The greatest coding skills won't help if your web content is full of misspellings and poor grammar. (Being dyslexic, I have no cammant!)
12) Click Here for Click Here - This is such a nice web application that you've built. It will really help our business deploy content to the web. And look it automatically creates links that say things like "Click Here", "More" and "Continue Reading." Now how do we change those to something more descriptive? We can't? Don't call us, we'll call you. (Use your Tool Tip and Alt tags!!!)
13) Putting up a Velvet Rope - This is such as cool web site, can I come in? Oh, you only let in people from the IE click? Us Safari geeks aren't welcome? And I was going to spend so much money. Don't you know that browser-specific web sites and applications are like so five years ago?
14) This is a Web Site, Right? - Now this is what I call a content rich site. Look at the useful information here. Let me click here, wait, this is a PDF document, and this is a Word document. I thought this was a web site, you know, something I could view in a web browser. (What is the point of providing a content managed Web site when half the content the user wants to view is hidden away in PDF and Word files? I bet 90% or more of content in Word and PDF that are available on the internet would be easy to provide on a Web page and if it was users would read it more!)
15) Over-crowding - You know, when people say that something is like finding a needle in a haystack, they don't mean that in a good way. On the web, too many links and other components can make it hard for a visitor to find the content that they want.