Out of curiosity I just re-authorised them for access and was displayed the following message:
"We're sad to announce that due to dwindling traffic, expensive hosting costs, and new limitations of the Facebook API, we've decided to close down Heyevent. We're sad to have to do this, but we unfortunatelu we see no other option. Since the launch of Heyevent, Facebook themselves has added more event recommendation. They're not as good as Heyevent's recommendations, yet. Hopefully they'll get better. Thanks for using the service!"
I found it somewhat useful in the past to keep using facebook to a minimum, so I wish them the best.
There must be some other areas of data based servicing that experience difficulties that but I can't think of any other right now.