You know what really grinds my gears? Logins on websites. There are a lot of websites that I login to and want to use. The sites that my browser remembers, I use a lot. When a site is set up with fancy login popup windows or something, then my browser (Firefox) doesn’t somehow remember them, so I don’t use those sites as often as I’d like. It’s a hassle to login.
Two sites that come to mind right now are Digg.com and Technorati.
And if your site is set up to be work like the norm, then at least name your login fields correctly. If it’s really a username, then say username but if my username is my email address, then say "Email Address" instead of "Username". This will help me search my email and wherever else so that I can take my precious time and track down what I need to so that I can login and contribute to your website.
As a web developer myself, this irks the heck out of me. Most tech savy people are going to use FireFox over Internet Explorer, but you do want to make sure your sites work with both. Make it easy for people to use your website and you’ll get more interaction… which is something you want (cough… Kevin Rose).
And that’s what grinds my gears. Tom?