Yesterday we ran a post about Cubeduel, a service that mixes the best (or worst) of Hot or Not with LinkedIn. Fire up the site and it will show you photos of two coworkers — pick the one you’d prefer to work with, and Cubeduel will present you with another pair of photos. It’s addictive, a bit evil, and has skyrocketed in usage over the last few days since it launched. Unfortunately, it took off a bit too quickly.

The service went down earlier today for reasons that were initially unclear — did LinkedIn block the site because it ranks coworkers in a way that isn’t exactly flattering to everyone, or did the site just get too popular, too fast? Turns out it’s the latter — Cubeduel has exceeded LinkedIn’s API limits (which is what one of the site’s creators, Tony Wright, initially guessed). Here’s an explanation from LinkedIn Director of Communications Hani Durzy:

We did not shut Cubeduel down. The application was using our open LinkedIn Developer Platform, which has a daily access limit that is publicly documented. Our developer platform limits are designed to protect our members, and have been in place since the platform program was introduced a year ago. We are in communication with the people behind Cubedeal to discuss how they can move forward. We are always interested in seeing our platform used in creative, innovative new ways by developers.

I followed up by asking if the site might be allowed to exceed the standard API limits, or if Cubeduel would have to find a way to restructure the site to fit within the normal constraints. The answer to that isn’t clear — Durzy says they’re still talking to each other.

Wright says that before the API limit was hit Cubeduel was far exceeding his expectations — he told me yesterday the site would get “hundreds of thousands” of ranked users by the end of the week. Now he says they were “well on our way to millions” before the API limit kicked in.