Nothing happened to them, they're still there. But they apparently changed search engines.
For a while now I've been using a9.com as my main search engine. I'm not sure why exactly, mostly just force of habit plus their toolbar seems to catch my eye more often than the Yahoo or Google toolbars. I figured they're OK because they're basically a value-added front end to Google.
On Tuesday of this week (today's Thursday but I'm a slow blogger) I noticed that the default search engine now is Microsoft's live.com. I didn't see any announcement that they're changing, but I wasn't really paying attention.
I don't object or anything. In fact this will give me a chance to try out the live.com search engine without having to actually go there. Maybe it's better than Google.