The web has been around for a good while. Still many little things are more often wrong than right. We should do better.
Here's a list of little, easily fixable things that greatly affect the user experience.
When you have a signup form, don't restrict the complexity of the password. Your system should support long and complex passwords, it makes for a really crappy first experience when users get their crafty passwords rejected by your picky system.
Kill paginated articles. We know how to scroll. Only reason you would need to paginate content nowadays is to squeeze out more page views. That is pretty damn evil.
Create proper links for phone numbers. A tap should make a call, so that there is no need to copy paste or memorize numbers. Selecting that number and then copy pasting it on a smartphone is not that easy.
Log in the user after they sign up for your service. Demanding users to input their login info again right after they just gave you the same damn info starts the relationship on a bad note. You just look lazy.
Log in the user also when they have just changed their password. No need to force a login again.
Don't shoot pop ups at user's face when they're engaging with your content. Ask them later. Popups might get more results, but the people on those lists often just gave their email to get rid of your pop up. They're not a quality audience.
And if you really must use a pop up to annoy the crap out of your users, don't make them have to click on a text that says something like "No, I suck and I don't want to be a good person". That drives people away.
Remember shopping cart content when people sign up to order on your ecommerce site. Not many things suck as much as having to find all that stuff again.
Make your forms remember the content, so when a user accidentally closes the tab or navigates back - all is not lost. Everyone knows the feeling when you go "oops" after 15 min of writing. You can be a real hero here!
Save the email address or user name when navigating from the login form to the forgot password form. Why would you want to make your user retype that?
Remember that trust and loyalty is built slowly, one small happy experience at a time.
We tweet about user experience in the web, you can follow us at http://twitter.com/wingmenguys for more. :)