Sites which force you to open an account just to buy one thing
The title says it all, in this case. You'll recognise the scenario. You track down something on the web, like the price and click on 'Buy'. Next thing you know is that you're being told that you have to 'open an account' with the site/company before you can proceed with checkout. It's not so much the time taken to enter your details - you'd have to do that anyway, so that they know where to send the goods - it's that you've then got one more username and password to remember, to add to the 218 you already juggle in your head (or, if you're smarter, in an encrypted database on your PC or smartphone/PDA). And it also means one more company holding on tightly to your personal information. Look, I just want to buy this ONE item! There's nothing else on your site that tempts me. Yes, I'm sure, just let me buy it, and no, I really, really DON'T want to open a permanent account. Good sites, of course, make the account bit optional.