According to an email from Hot or Not’s founders, since moving to a free model the site had become inundated by spam:
You also warned us that this would probably lead to more spammers and fake profiles. You were right, this is exactly what happened. The spammers got aggressive to the point where they were screwing up the system, even causing the “someone wants to meet you” emails to not be sent for periods as long as 5 days.”
As before, Hot or Not will now have a free level of membership then a paid tier for sending messages to profiles.