I have a new pet hate. Well, really a newly resurfaced old pet hate... On websites, of course:
That. It's an empty input with a 'go' button. Really user friendly
It is, of course, a search box. Clearly many web designers think that this should be obvious to your average internet user. It's not. It's just an unlabelled input box.
This particular example was screengrabbed from the Ubuntu forums, and they really should know better.
I'm not making any claims of expertise when it comes to doing user friendly accessible websites, but I do my best - and things like that really annoy me. Like having next/previous/first/last page links in the 'wrong' order. grr.