- Advertisements. I understand your need to get the money in, but do it with decency. Don't clutter my screen with flashing and blinking crap, don't have ads appear over an article I'm just trying to read and don't mess up the formatting so much I can't figure out where the text continues. Also, if it is an advertisement, call it an advertisement. Don't call it a "welcome screen" or a "hello from our sponsor," who are you trying to fool? I have to disappoint you though, the only instances I click on ads are accidentally. If I want product information, I know how to get it, and it's not on your website. As far as I am concerned product placement on websites is entirely useless.
Example: Forbes. Try reading a single article without going insane.
- Emails. Never ever send me emails I didn't ask for. And no, I am not interested in your news, your updates, or your great community events. It is totally sufficient if I learn of that next time I log in. If there is such a time. The services I am most pleased with are Google, Twitter and Facebook. I never received a single email from them that I didn't ask for. Make "no emails" the default and don't cheat by requiring me to uncheck a dozen different boxes.
Example: Bank of America. Even though I complained several times already when I was a customer, they still send me advertisments after I finally managed to close all my accounts. Same with United Airlines, SiteMeter, Neon, and a dozen other websites that require subscription and then clog your inbox with html emails.
- Over-the-top Security. Unless you are indeed storing sensitive information, don't ask for 8 digit passwords containing numbers, letters and special symbols. Don't suspend accounts if users guess a wrong password three times if the only thing you're protecting is their nickname. Don't ask for information that's none of your business to begin with. Btw, I don't actually live in Algeria and my birth year isn't 1962 either. Also, have an option for password recovery that doesn't require the registered email address. I have a couple of dead accounts because the email address I used to register is no longer active and I can't recall the password. Yet, the reminder is sent to that address.
- Can't delete my account: Have an option to delete an account. It might hurt, but there are people who figure out they don't want your service after all. If you don't have this option users who want to leave will just scramble up their profile information and log out a last time, leaving you with a dead account. At the very least, clean up your inactive accounts every now and then.
- Clutter overdose. Don't clutter your website with a thousand flash animations, widgets, java-scripts and other stuff. Keep it simple. Why do you have the weather forecast on your site? If that's what I'd be looking for, I'd be looking elsewhere. Also, it is self-evident but can't be repeated sufficiently often: please use a clear and intuitive layout that is the same for all sites showing the location in the menu tree. And please do mark visited links in a different color. To achieve that purpose, don't hesitate to copy templates from highly frequented websites and modify them slighthy to meet your needs. That's how natural selection works.
- Sound effects. The surest and fastest way to get me off your site is background music, ads with sound effects, or speaking avatars. Especially bad if the sound can't be turned off. Look, I might not be alone, I really don't want my computer to make embarrassing noises, okay?
- Browser incompatibility. You'd think that's the first thing everybody learns who designs websites: different browsers will interpret your template differently. Have a look at it at least with MS Internet Explorer, Safari, Firefox and Google Chrome. Or have somebody else look at it who uses these browsers and send you a screenshot. You'll be shocked how crappy your website suddenly looks.
Example: The ESTA website that couldn't be opened with Google Chrome (they meanwhile fixed the problem).
- Local lingo. If you're hosting a forum, don't invent your own html encoding. Just let users enter html tags and screen for unwanted tags. How I am supposed to recall if you want [ .\] for a link or ".":., or *.* is italics or maybe boldface? Example: NatureNetworks. Can never recall how to enter a link. Also, don't give fancy names to menu items that nobody knows what they mean. What is "avant garde" or "horizons" supposed to be?
- Who the fuck are you and what do you want? Don't force me to go to Whois to look up who you are. Have an "about" and a valid contact address. I want to know who you are, what your background and your motivation is. Everything else smells fishy unless you have a good reason to maintain anonymity - and if you have that reason I want to know it as well. Also, tell me upfront what you do. For example, if your "international" company doesn't ship anywhere but in the USA, tell me before I've spent half an hour putting items in your cart.
- Your scripts suck! Prepare for failure: If you have any forms on your site, always, always, always, provide a message confirming the script was executed properly. The message should contain all the submitted information together with an option for correction in case there's a problem. Further, keep in mind people's information might not fit into your great form for whatever reasons. Canadian Zipcodes do not consist of 5 digits. Some people really don't have a home phone. Worst thing ever: If your script returns an error and I'll have to fill out ALL fields again.