If it is some random site I am visiting where I have not been before, I will much more likely login via Facebook Connect or OpenID than going through some registering (where I usually have to figure out what types of passwords it accepts, about a free username, and wait for an accept mail and all that through a terribly annoying and slow guidance).

I definitely agree that for some sites, the signup process is too entailed. For me though, the barrier is usually identifying myself rather than having to create a login. If the site has something compelling enough for me to identify myself to it, then it's not that big of a leap to create a username and password.

I've seen signup success rates between 30-97% with conventional login systems. There are two things that appeal to me about Facebook:

(i) people take their Facebook identities seriously, so they're less likely to be griefers, and (ii) the like mechanism to push back updates about items that have changed