Something's very wrong with the servers at mobile check-in start-up Foursquare, which had experienced problems on Monday morning and then ultimately crashed altogether and hadn't been resuscitated as of 8:00 p.m. PT.
Reached via e-mail, one of Foursquare's executives said the company was not yet willing to disclose the cause of the outage but promised that a postmortem blog post would explain the situation when it had been mitigated.
"The light at the end of the tunnel seems oh-so-close. Should have some good news soon!" a tweet from Foursquare's Twitter account read at about 7:30 p.m. PT on Monday.
Foursquare's service has gone on the fritz for notable periods of time--much as Twitter's did when it was coping with hype and fast user adoption coupled with a low employee headcount and insufficient server power--but this is potentially its longest outage to date. It's a precarious time for the Foursquare service to be down, considering it now has its most formidable rival yet in the Facebook Places product and needs to be sure that its user numbers don't take a hit.
Twitter had an outage of its own Monday, coincidentally right at the time then-CEO Evan Williams announced he was stepping aside to focus on product strategy rather than running the company.
UPDATE (8:35 p.m. PT): A Foursquare employee tells CNET that the service recently was restored and that the company is "still monitoring" its stability.