Enforced, immediate registration. Requiring a new user to register and provide a modicum of information is a reasonable request, just do it after you've sucked the person in. Most sites require that registration is the first step, and this puts a barrier in front of adoption. At the very least, companies could ask for name and email address but not require it until a later time.
Impossibly long URLs. Many sites generate URLs that are longer than ninety characters. When you copy, paste, and email this URL, a line break is added, so people cannot click on it to go to the intended location. For example, the URL for a billiard table sold on the CostCo site had 300 characters. Just how many billiard-table models could CostCo be selling? This can't be necessary.
Unreadable confirmation (CAPTCHA) codes. Don't get me wrong: I don't support spam or robots creating accounts. A confirmation system is a good thing, but many are too difficult to read: upper versus lower case, I vs 1, and 0 versus O. My theory is that technology is called CAPTCHA because it captures folks in an endless loop of trying to prove to a machine that you're a human.
Emails without signatures. In email lingo, a signature is text that is automatically included in every email you send. Typically, it contains the person name, email address, phone numbers, and web site. This is very useful if someone wants to pick up the phone and call you or visit your website without having to ask for that information.
Windows that don't generate URLs. Have you ever wanted to point people to a page, but the page has no URL? You've got a window open that you want to tell someone about, but you'd have to write an essay to explain how to get that window open again. Did someone at the company decide that it didn't want referrals, links, and additional traffic?
Lack of a search function. Some sites that don't allow people to search. This is okay for simple sites where a site map suffices, but that's seldom the case. If your site has a site map that goes deeper than one level, it probably needs a search box.
Lack of ways to share an experience. It's hard to make a product, service, or web site that's so compelling that people want to share it. If you do, it's a shame when there's not an easy way for people to spread what they like. The next time you're visiting a web site, look for buttons that say "Share this" or "Email this to a friend" and implement similar functionality.
Limiting contact to email. Don't get me wrong: I live and die by email, but there are times I want to call a company or maybe even snail mail something to it. Many companies only allow people to send an email via a web form. Why don't companies call this page "Don't Contact Us" and at least be honest? Many companies don't even list a way to contact it at all, so I guess there are still dumber people out there.
Lack of feeds and email lists. When people are interested in your company, they will want to receive information about your products and services. This should be as easy as possible, meaning that you provide both email and RSS feeds for content and PR newsletters.
Requirement to re-type email addresses. I have 8,000 email addresses in Entourage. I am not going to re-type them into the done-as-an-afterthought address book that companies build into their products. If nothing else, companies can use this cool tool from Plaxo or allow text imports into the aforementioned crappy address book. When do you suppose a standard format will emerge for transferring contacts?
User names that cannot contain the '@' character. In other words, a user name cannot be your email address. I am a member of hundreds of sites. I can't remember if my user name is kawasaki, gkawasaki, guykawasaki, or kawasaki3487. I do know what my email address is, so just let me use that as my user name.
Case-sensitive user names and passwords. I know: user names and passwords that are case sensitive are more secure, but it increases the likelihood of incorrectly typing one's user name and password. A common occurrence in many a demo is when a company's CEO can't sign into her own account because she didn't type the proper case of her user name or password. You'd think people would get a clue from that.
Friction-full commenting. "Moderated comments" is an oxymoron. If your company is trying to be a hip, myth busting, hypocrisy-outing organization, then it should let anyone comment.
People in Asia say, "Buddha is in the details." Adoption is in the details too, so take this list and check it twice to ensure that finding, buying, and using your product or service is as friction-free as possible. The scary thing is that as I compiled this list, I saw that my own site (Alltop) violated some of the items. I need to get cracking on this.
Excerpted from my next book: Reality Check Outsmarting, Outmanaging, Outmarketing Your Competition