My favorite CAPTCHAs are when they don't state whether they're case-sensitive or not and it's hard to tell whether some characters are uppercase or lowercase.
6 minutes? Seriously? You guys must be pretty motivated.
I gave up after about 30s. I'd probably have given up after 60s, even if there was a prize at the end (e.g. being registered). I rebel violently when confronted by a UI crime-scene like that. I'm feeling ill after just two pages of that form.