I think we all agree that we need -some- form a protection against spambots automatically signing in to gmail accounts, posting annoying links in webforms, etc. But man, there's got to be a limit. Captcha's are generally considered as a "bad user experience", and should be avoided as much as possible. These guys didn't take the hint.
And Rapidshare wins the prize for most unreadable captcha -- or am I just too stupid to see the difference between a cat and a dog?
Or let's distinguish colors. No wait, let's blur them out completely first, then let the user try to decipher them. That had to be the reasoning behind this one.
Or how about this one, used in a guestbook. Seriously, just close the damn guestbook -- no one will post in it.
And then there's the complete riddle. These are the kind of tasks you expect in a quiz, not to place a comment on a website.
The last one could be considered fun, if you have some free time and want some brain-puzzles to figure it out. I bet it gets a whole lot more annoying if you have to enter that one 10 times a day.