
You may not have used Second Life's Map API. I know I didn't frequently, though I'd just started using it for a project yesterday. Today? It's gone, without any apparent warning - I noticed a few minutes ago when I sat down to continue yesterday's work.
Some hurried checking around looking for notices or announcements from Linden Lab (there aren't any) indicates that the talented Katharine Berry has also noticed the problem, and that it's killed the AJAXLife project. She writes, "Some research indicates that they have intended to do so for a while, and were going to make a wide announcement before doing so. Breaking it does not count as a wide announcement."
There are apparently undocumented ways to pull some of this data through the SL-CAPS capabilities web-services, but they may be incomplete and seem to rely mostly on guesswork.
Whether the Map API is down intentionally or unintentionally, this counts as a communications failure, I should think.