Custom website design prefer dazzle over function. Function is boring. Who wants a simple text link when a pop up Javascript navigation bar impresses the client? Every web page needs recognizable, underlined text links on every page, preferably top and bottom. Don't make me waste time trying to find the internal page I am really looking for.
Poor contact information is a binary pair of bad navigation. How many sites have you been to where you cannot find a phone number, a street address, or even an email address? I think it's sweet that you put up an email contact form on your site, but I prefer to use my default email compose screen. Every web-based email form is different. I don't want to waste time learning to use your form when my email client works fine.
There is no excuse for this one. If you have a large website with dozens or hundreds of pages, give me an internal search box to find what I need. Google and Yahoo! and many others will give you the tool - free - to put on your site. Use it. I don't want a website to dictate how I experience their site. I am a guest on your site. I don't need to come back to your page when I hit the back button. That's why I hit the back button in the first place. You don't have the information I am looking for. In a similar vein, I don't like to see other right click functions like "view page source" disabled. I don't need to steal your HTML code, but if I want to, disabling right click will not stop me. I might want to see how you achieved a certain formatting effect. If I am impressed, you can bet I'll be back. Pet peeves take many forms online. No list like this is complete, but any webmaster that can avoid these 10 major annoyances is a hero in my book.